TECHNICAL ADVANCEMENTS 

AND ISSUES ASSOCIATED WITH 

THE PERMANENT DISPOSAL OF 

HIGH-ACTIVITY WASTES 

Lessons Learned from Yucca Mountain 

and Other Programs 

June 2011 

A Report to Congress 

and the Secretary of Energy 

United States 

Nuclear Waste Technical Review Board 

U.S. Nuclear Waste Technical Review Board 

TECHNICAL ADVANCEMENTS AND ISSUES 

ASSOCIATED WITH THE PERMANENT 

DISPOSAL OF HIGH-ACTIVITY WASTES
 

Lessons Learned from Yucca Mountain 

and Other Programs 

June 2011 
ACKNOWLEDGMENT
 

Allen Croff, John Kessler, Peter Swift, and Chris Whipple reviewed a near-final version of 

this report and made many helpful comments. We took their comments into consideration 

while producing the final version of the report. We believe that the accuracy and clarity of 

the report are improved because of their comments. 

We are extremely grateful to the reviewers for the time and effort that they spent in 

reviewing the report, for the care that they used in conducting their reviews, and for their 

comments and suggestions. Any inaccuracies or errors in the report are our responsibility, 

and the views and conclusions expressed in the report are those of the Board and not 

necessarily those of the reviewers. 
U.S. NUCLEAr WASTE
 

TEChNiCAL rEviEW BOArD 

2011 

B. John Garrick, Ph.D., P.E., Chairman 

Consultant 

Laguna Beach, California 

Mark D. Abkowitz, Ph.D. 

Vanderbilt University 

Nashville, Tennessee 

Thure E. Cerling, Ph.D. 

University of Utah 

Salt Lake City, Utah 

George M. Hornberger, Ph.D. 

Vanderbilt University 

Nashville, Tennessee 

Ronald M. Latanision, Ph.D. 

Exponent Corporation 

Natick, Massachusetts 

William M. Murphy, Ph.D. 

California State University 

Chico, California 

Wm. Howard Arnold, Ph.D., P.E. 

Consultant 

Macatawa, Michigan 

David J. Duquette, Ph.D. 

Rensselaer Polytechnic Institute 

Troy, New York 

Andrew C. Kadak, Ph.D. 

Exponent Corporation 

Natick, Massachusetts 

Ali Mosleh, Ph.D. 

University of Maryland 

College Park, Maryland 

Henry Petroski, Ph.D., P.E. 

Duke University 

Durham, North Carolina 
NUCLEAr WASTE

TEChNiCAL rEviEW

BOArD STAff

EXECUTIVE STAFF 

Nigel Mote Executive Director 

Joyce M. Dory Director of Administration 

TECHNICAL STAFF 

Carlos A. W. Di Bella Senior Professional Staff 

David M. Diodato Senior Professional Staff 

Bruce E. Kirstein Senior Professional Staff 

Daniel S. Metlay Senior Professional Staff 

Douglas B. Rigby Senior Professional Staff 

Gene E. Rowe Senior Professional Staff 

Director 

EXTERNAL AFFAIRS STAFF 

Karyn D. Severson 

INFORMATION TECHNOLOGY STAFF 

William D. Harrison Systems Administrator 

ADMINISTRATIVE & SUPPORT STAFF 

Davonya S. Barnes Information Systems Specialist 

Linda J. Coultry Program Management Specialist 

Linda L. Hiatt Management Analyst 


1

TEChNiCAL SUMMArY
 

iNTrODUCTiON 

The U.S. Nuclear Waste Technical Review Board was created by Congress in 1987 to evaluate 

the technical and scientific validity of U.S. Department of Energy (DOE) work related to 

implementing the Nuclear Waste Policy Act. The Board’s major focus for the last 20 years has 

been on DOE’s efforts to develop a deep geologic repository for high-activity waste† at Yucca 

Mountain in Nevada. As this report is being written, the Administration has eliminated 

DOE’s Office of Civilian Radioactive Waste Management and is seeking to withdraw the 

license application it submitted to the U.S. Nuclear Regulatory Commission to construct a 

repository at Yucca Mountain. 

An important part of the Board’s mission is advising Congress and the Secretary of Energy 

on technical issues related to management and disposal of high-activity waste. Therefore, 

regardless of the outcome of deliberations over Yucca Mountain, the Board believes that it 

is important to extract knowledge while it is still available from the experience of the Yucca 

Mountain program and other programs. Such knowledge may be useful for future U.S. highactivity waste management and disposal efforts. 

This report is not meant to be an assessment of the licenseability of a Yucca Mountain 

repository. If licensing goes forward, the Nuclear Regulatory Commission will determine 

whether a license should be granted. But, as President Harry S Truman astutely observed, 

“...there is nothing new in the world except the history you do not know.” The purpose of 

this report, then, is to extract from the history of the Yucca Mountain program, and to a 

lesser degree from other programs, some of the technical “lessons learned” that may apply to 

future U.S. programs for waste management and waste disposal. 

LONG-TErM MANAGEMENT Of hiGh-ACTiviTY WASTE— 

TEChNiCAL ChALLENGES 

Perceptions of and opinions on managing high-activity waste vary from it being a problem 

that is the Achilles’ heel of nuclear power without a real solution to being a trivial technical 

problem that is made complicated by mismanagement, inconsistent policies, or political 

† The term “high-activity waste” refers to both high-level radioactive waste and spent nuclear fuel. 

Technical Summary i 
decisions. Experience indicates that managing high-activity waste is a problem that is 

neither unsolvable nor trivial. An international consensus has emerged that burial of highactivity waste in a deep geologic repository is technically feasible and that such an approach 

can provide adequate protection to humans and the environment. 

At least at this time, the only potential alternative to deep geologic disposal of high-activity 

waste is partitioning the material and transmuting it in reactors or accelerators. Although 

partitioning and transmutation theoretically could reduce waste volumes, there are many 

practical problems, the solutions to which are still very much a challenge. Moreover, no 

amount of partitioning and transmutation can completely eliminate the need for deep 

geologic disposal. All fuel cycles generate long-lived radioactive wastes that cannot be 

completely destroyed. 

The overarching complication of all high-activity waste-management programs is the longlived toxicity of the waste, which requires isolating it from biological systems, especially 

human beings, for many hundreds of thousands of years. Understanding the potential 

performance of a proposed geologic repository is complex because repository performance 

depends on (1) the integrity of the engineered barriers, including the waste form and its 

physical state; (2) dissolution and mobilization mechanisms within the engineered barriers; 

(3) transport, retardation, and sequestering processes in the natural system; and (4) 

biological uptake. The waste form and heat generated by the wastes are two critical factors 

affecting basic understanding of a geologic repository. The waste form greatly affects the 

chemistry when radionuclides are mobilized, and heat generation introduces uncertainties 

in the analytical models, particularly at temperatures above boiling. 

Three categories of radioactive species dominate design considerations for a geologic 

repository. The first category consists of 90Sr and 137Cs. Although they are not considered 

a long-term repository health risk because of their relatively short half-lives, they are the 

dominant contributors to the heat released by spent nuclear fuel during the first hundred 

years after irradiation. They also are a major part of the radiation source to be considered in 

handling, storage, and transportation operations before disposal. Decay heat can be a major 

issue in repository design if there are limits on the size of the repository. The second category 

of radioactive species important for repository design comprises the fission products 

99Tc and 129I. These fission products are very long-lived and are in some abundance in the 

inventory. They are generally soluble and thus able to migrate relatively quickly on release 

to groundwater. The third category is from the actinide group of radioactive species. The 

important actinides include uranium, plutonium, neptunium, and americium. Many of 

these species also are long-lived. 

The very long half-lives of many of these species present major challenges to demonstrating 

waste isolation and containment. Because movement by or through water is the dominant 

ii Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
mode by which radionuclides can reach the accessible environment, geochemical mobility is 

a principal concern. Projections have to be made about the solubility limits for each species 

as well as for which ones will move as colloids. The projections may have to extend far into 

the future, perhaps as much as one million years. 

LESSONS LEArNED frOM ThE YUCCA MOUNTAiN PrOGrAM 

The United States has a variety of waste forms with different chemical and physical 

properties because of their generation through defense activities, reactor-development 

work, and electricity production. Specialized deep geologic disposal methods that take 

advantage of these differences may be reasonable to consider. A possible scenario is using 

deep geologic repositories that permit retrieval of spent nuclear fuel and boreholes that 

preclude retrieval of waste forms that offer few or no further recycling advantages, such as 

vitrified high-level waste. 

High-activity wastes in the United States are in a wide variety of forms and in some cases, 

such as much of the liquid “legacy” waste from the Manhattan Project and the Cold War, are 

difficult to recover from storage and convert to suitable solid forms for permanent disposal. 

The waste form determines the burden on the engineered barrier system and the natural 

system of a geologic disposal facility. Thus, there are three options: (1) develop disposal 

systems that can accommodate a wide variety of waste forms; (2) process or package the 

wastes into more-or-less standard forms for disposal; or (3) develop separate repositories for 

classes of waste forms, e.g., deep boreholes for vitrified waste and a deep geologic repository 

for spent nuclear fuel. Waste-form characteristics and inventories should be reevaluated, 

and the issue of the optimal disposal method for each waste form should be assessed. The 

one-size-fits-all approach used by the Yucca Mountain program may or may not be the best 

approach. Decisions still are being made on these issues, and a timely decision on geologic 

disposal siting could have a major effect on the availability of a permanent solution for 

disposal of high-activity waste. 

Considerable methodology and evidence have been developed to indicate the technical 

feasibility of isolating nuclear waste in an unsaturated zone of the subsurface that involves 

an oxidizing environment, thus expanding the options for siting a repository. Programs both 

inside and outside the United States have provided evidence that many geologic options can 

be attractive candidates for a repository, including intrusive or extrusive igneous rocks (e.g., 

granite, tuff) and sedimentary rocks (e.g., salt, clay). 

Studies at Yucca Mountain advanced scientific understanding of water flow in unsaturated 

fractured rock in arid regions. On the basis of laboratory, field, and analytical work, 

scientists developed models accounting for runoff, evaporation, plant transpiration, the 

effect of capillary forces, and other parameters. Various hypotheses were tested in the 

Technical Summary iii 
models, leading to improved insights on flow in unsaturated rock. Yucca Mountain scientists 

also coupled heat and fluid-mass transport with provision for geochemical reactions in 

time and space. That coupling allows modeling on time scales that are appropriate for 

considering disposal of nuclear waste and sets the stage for future advances in modeling and 

understanding multiphase transport in geologic media. 

The Yucca Mountain program contributed to knowledge of how to use mapping and other 

studies for locating faults and past volcanic activity in the vicinity of potential disposal 

locations. The location, timing, and amount of movement of these faults and of periods of 

volcanism were characterized as part of the hazard analysis. The Yucca Mountain program 

significantly advanced the state of scientific knowledge in several areas, including its 

rigorous leading-edge investigations of seismic and igneous hazards. State-of-the-art expert 

elicitations and probabilistic seismic- and volcanic-hazard analyses led to significantly morerobust fundamental understanding of the phenomena and substantially improved technical 

bases for risk calculations. A diagnostic science was developed based on using precariously 

balanced rocks as strong-motion seismoscopes at the Earth’s surface to constrain the 

probability of seismic ground motions. 

Yucca Mountain engineers and others investigated many alternatives for controlling 

the temperatures in the repository. Many of the alternatives were quite novel. The work 

established that there are many ways to meet thermal goals and constraints from which to 

select for developing an optimal system. The decision on a repository’s temperature limit is 

one that future repository developers face, and it is a difficult one to make. 

Contemporaneously with the Yucca Mountain program, similar advances in understanding 

geologic disposal in crystalline rock, clay, and salt were being made in other countries. Taken 

together with the American experience, these activities and the data and understanding from 

them constitute a formidable knowledge base for pursuing geologic disposal in many media. 

Research over the last several decades has led to increasing confidence in the ability to 

provide engineered barriers that will delay dependence on the waste-isolation capabilities 

of the natural system for extended periods, possibly hundreds of thousands of years. Such a 

delay dramatically reduces the radiotoxicity of the waste and simplifies the chemistry of the 

waste that might enter the natural system, thus enhancing the predictability of the long-term 

performance of a repository. 

Assuming that the environments, including temperatures, to which waste packages would 

be exposed over time in a repository are known or bounded and that appropriate corrosion 

data are available, the general-corrosion behavior of waste packages over long periods is 

predictable. More difficult to predict are localized-corrosion rates. The ability to control 

waste package materials and fabrication methods enhances confidence in the analysis 

iv Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
and prediction of waste package lifetimes. Analyses indicate that the lifetime of the waste 

package can be very long, if the waste package also is robust (thick-walled). Because of 

the long-term predictability of waste packages and the positive experience of programs in 

crystalline rock in reducing environments and tuff in oxidizing environments, the Board 

recommends that future repository programs in the United States at least consider robust 

waste packages. This is believed to be an effective way to reduce uncertainty in the overall 

performance of a repository, regardless of the site chosen. 

Because waste package design and performance depend critically on environment, studying 

the evolution of the waste packages’ surface environment is important for any future 

repository. For example, an issue for the waste packages in the proposed Yucca Mountain 

repository was the possible existence of elevated temperatures in combination with liquid 

water in the form of concentrated, multicomponent brines, which are a result of exposure to 

dust-containing ventilation air from the outside. The Yucca Mountain experience should be 

valuable for future designers of waste packages, particularly with respect to the requirements 

for demonstrating long-term performance. 

Clay-based buffers, fillers, seals, or plugs are used in many repository concepts, and clay is 

the geologic medium for some proposed repositories overseas. Because swelling clay may 

play an important role in any future U.S. repository, future U.S. programs should be aware 

of, and become involved in, cooperative international research efforts on buffers, backfills, 

and other uses of swelling clays. 

A critical factor in assessing the performance of a geologic repository, and thus the achievement 

of an efficient design, is quantifying the radionuclide source term entering the natural system. 

Experience indicates an imbalance in the relative emphasis on research in degradation of the 

engineered barriers and the emphasis on research in mobilization of the waste. 

A key calculation of the performance of any repository is the release rate of radionuclides 

from the engineered barrier system to the natural system as a function of time: the source 

term. An overarching lesson learned in the Yucca Mountain program is the difficulty of 

quantifying the properties important to the mobilization and transport of radionuclides. 

The modeling and simplifying assumptions for radionuclide mobilization and transport 

in the engineered barrier system were conservative—possibly resulting in an unrealistic 

characterization of the source term. There are several areas where more-detailed 

analysis would have resulted in a more transparent if not a more realistic source term. 

They include more-accurate characterization of the coprecipitation of radionuclides in 

thermodynamically stable secondary minerals and more-explicit consideration of the rate of 

diffusive transport of radionuclides through waste-package-alteration materials to account 

for the transient retardation of radionuclide migration to the natural environment. 

Technical Summary v 
Another area of considerable interest has to do with the possibility of localized reducing 

conditions in an otherwise oxidizing environment. In particular, the presence of abundant 

reducing material in the engineered barriers and the ability of corrosion products to limit 

the access of water and oxygen to the waste are likely to cause substantial lowering of the 

in-package oxidation-reduction potential. For example, despite strong evidence that the 

presence of large amounts of iron-based waste-package or invert materials significantly 

reduces the rate of degradation of uranium dioxide or spent fuel by making the local 

environment less oxidizing, DOE only partially took the effect of these materials on the 

environment into account in its license application. 

Future consideration of sites involving unsaturated zones will greatly benefit from the 

Yucca Mountain experience, particularly for modeling the mobilization and transport 

of radionuclides. The studies and investigations associated with the retardation of 

radioactive-material transport in the Yucca Mountain performance assessment were a major 

contribution. 

There is strong evidence that many of the Yucca Mountain program deficiencies could have 

been prevented had the project adopted a total integrated systems approach to performing the 

necessary science, engineering, and construction activity. A critically important element of 

such an approach is making the right decisions on transitioning from a science program to an 

engineering program that involves prototyping first-of-a-kind systems. 

Although a total system simulation model that included waste acceptance, storage, handling, 

transportation, packaging, and emplacement was developed for the Yucca Mountain 

program, it was not fully embraced by all program elements until late and was terminated 

too early. Such models are key to a systems approach to design and to ensuring that all 

the elements of the program are appropriately integrated. Different scenarios should be 

considered that account for such realities as waste handling and transportation issues, 

construction delays, operational upsets, failures to meet performance goals, and changes in 

throughput. Future programs must take integration of the entire system (including reprocessing 

and recycling, if undertaken) into account at the outset and must maintain that perspective 

thereafter. Analyzing and evaluating a waste-management system as an integrated whole 

enables one to examine system throughput, identify possible choke points, and recognize 

where various design and operational elements are incompatible. Understanding this and 

taking it into account are essential for harmonizing cask design, fleet acquisition, handling, 

access and egress, line-haul operations, and other activities that must be carried out for the 

system to perform in a safe, secure, and efficient manner. Treating a highly interdependent 

system in a piecemeal and segmented fashion almost guarantees that all of its elements will 

not fit together effectively. 

vi Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
Because the transportation-aging-disposal (TAD) canister concept and the multipurposecanister concept proposed more than a decade before it offer safety and cost advantages, 

future programs should consider them carefully. The waste package size that was proposed 

for Yucca Mountain does not allow for direct disposal of loaded dual-purpose canisters 

without repackaging the spent fuel. Accommodating dual-purpose canisters at Yucca 

Mountain would have required a slight increase in the size of the Yucca Mountain waste 

package, a concept that should be considered seriously for future geologic repositories. 

The experience with TAD canisters and the fact that dual-purpose canisters currently 

used by nuclear power plant operators are too large for the Yucca Mountain design in the 

license application argue strongly for addressing the entire waste-management system as a 

whole, from at-reactor to final disposal, at the earliest possible stage of any new program. 

For example, for future repository programs, the implementer should ensure that there is 

compatibility between waste package sizes and the sizes of canisters used in dry-storage 

systems. DOE also needs to continue pursuing burnup credit vigorously, because it likely 

will be needed for disposal of spent fuel in any future repository. 

Because site selection, site characterization, and repository engineering are such different 

projects, consideration should be given at the outset to the appropriate skills, organizational 

form, and institutional form for each project. The Yucca Mountain program was a mix of 

science and engineering, with the resulting conflicts of authority and management of the 

two disciplines. In first-of-a-kind programs that involve new technologies, the transition 

between science and engineering is sometimes difficult to resolve. Nevertheless, the lesson 

learned is the importance of establishing the point at which the science part of the program 

assumes a supporting role to the engineering. In particular, once the project becomes an 

engineering project, the technical and scientific needs of the project should be driven by 

what it takes to engineer the project to its performance goals. The failure to accomplish 

the transition from science to engineering until late contributed to many engineering 

deficiencies in the Yucca Mountain program. 

An additional deficiency was the lack of continuity of management, personnel, and funding. 

Contractors came and went, and managers cycled in and out, while the amount of money 

available in the next fiscal year was always in doubt and seldom under the control of the 

management of the program. The principles of good engineering are well known and 

include the need for a dedicated organization while maintaining continuity of its personnel, 

especially of its management and principal engineers and scientists. 

Besides management issues, the Yucca Mountain program demonstrated the absence of a 

strong engineering culture, particularly in the lack of prototyping of many first-of-a-kind 

systems and equipment and the lack of a maintenance program for subsurface repository 

operation. Examples of prototypes that would greatly facilitate the design include the waste 

Technical Summary vii 
package; the waste package platform; novel instrumentation; any novel equipment used to 

emplace, move, or install other equipment items; and the underground assembly of the drip 

shield. An example of a subsurface maintenance program is controlling preclosure drift 

degradation to prevent its interference with the efficiency of preclosure operations. 

The Yucca Mountain program produced the most comprehensive, internationally peer-reviewed 

repository performance assessment covering a million-year timeframe. More generally, 

probabilistic performance assessments can provide a balanced assessment of contributors to 

risk and therefore should be used throughout the life of a program to guide the selection of a 

research portfolio. 

Although the performance assessment, known as the Total System Performance Assessment 

(TSPA), had shortcomings, many of the models developed for it were unique, and the 

performance assessment itself was a major contribution to assessing projects involving very 

long time periods. Although TSPA contained the elements of a traditional probabilistic 

risk assessment, it was much more tailored to demonstrating compliance with Nuclear 

Regulatory Commission regulations as opposed to simply answering the explicit question, 

“What is the risk?” The main contribution of TSPA was that it provided a benchmark 

for future studies. The scoping of the assessment for nominal and disruptive events 

and the treatment of uncertainty were outstanding contributions to the risk sciences. 

TSPA demonstrated that probabilistic, dynamic modeling of large, complex natural and 

engineered systems can be performed. A critical output of TSPA was an importance 

ranking of the radionuclides contributing most to the long-term radiation doses at the 

accessible boundary of the repository. Such output would be extremely valuable for future 

consideration of chemical separation of radionuclides to simplify repository designs. 

An issue with TSPA, however, was its technical complexity in terms of building confidence 

in the results. Clearly, a version of TSPA that communicates better with both a technical 

and a public audience would greatly enhance its interpretation and value. An example of a 

feature of TSPA that could make it more transparent would be to avoid using probabilityweighted doses. Rather, the more traditional approach of calculating the risk of specific 

doses would be more in keeping with practices in the risk sciences. 

Another issue of great importance is how well TSPA represents reality. The inclusion 

of an uncertainty analysis of parameters and assumptions is critical in this regard. This 

was a major contribution of TSPA, but questions remained about the degree of reality in 

the models. The developers of TSPA sought to answer this concern with a performancemargin analysis to evaluate the importance of selected claimed conservatisms. Although 

this was very helpful in improving the transparency of the analysis, there still were some 

shortcomings. For example, the analysis would have been much more meaningful if it had 

addressed the effect on repository performance of taking credit for spent-fuel cladding. 

viii Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
Despite the limitations of TSPA, any future attempt to develop a repository at a location 

other than Yucca Mountain should embrace the principles of systems analysis by including 

risk assessments for both site selection and site characterization. Trade-off studies should be 

performed to help determine the preferred geologic media or repository types for each waste 

form. Additional trade-off studies should evaluate whether processing the waste form or 

reengineering the engineered barrier system would be beneficial, depending on the geologic 

media in which disposal is contemplated. 

MOviNG fOrWArD 

The knowledge base for geologic disposal of high-activity waste has greatly increased during 

the last couple of decades. In particular, the experience gained in the Yucca Mountain 

program on tuff as a repository medium in an oxidizing environment and the knowledge 

gained in other programs in other geologic media and reducing environments have 

established a very strong technical base for moving forward with geologic disposal in the 

United States. A first step would be ensuring that the current technical experience base from 

the Yucca Mountain program remains readily available and accessible. 

Realizing the full benefit of the advanced state of knowledge also requires renewing 

international cooperation by forging and maintaining strong bonds with the programs of 

other countries for waste management and disposal, both directly and through the auspices 

of the International Atomic Energy Agency and the Nuclear Energy Agency. Implementers 

of new U.S. repository efforts should increase attention to the advanced repository 

programs of Finland, France, Germany, Sweden, and Switzerland. New U.S. repository 

efforts involving site selection should examine the site-selection experience of the advanced 

programs as well as the activities of other nations currently selecting sites. The diversity 

of geology being considered worldwide is especially significant to the decision-making 

of the United States on future programs. The collective Yucca Mountain, Waste Isolation 

Pilot Plant, and international experiences to date strongly suggest that repositories can be 

developed in many geologic media. Deciding factors for site selection, therefore, may well be 

nontechnical. 

The Board believes that keeping a focus on a permanent solution is critical regardless of 

what interim measures for managing high-activity waste are charted. Among the reasons 

are (1) a permanent solution is needed under all foreseeable circumstances; (2) a permanent 

solution is critical to building public confidence that there is a way of isolating nuclear 

waste radioactivity from the biosphere to acceptable levels; (3) undue delay in a permanent 

solution could make tenuous a concept of waste management dependent on institutional 

stability; and (4) experience indicates that deploying a permanent solution to isolating highactivity waste could take decades. These reasons are believed to be compelling for a focused 

effort to implement a permanent solution for disposing of high-activity waste. 

Technical Summary ix 

Contents xi

TECHNICAL SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .i

Long-Term Management of High-Activity Waste—

Technical Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .i

Lessons Learned from the Yucca Mountain Program . . . . . . . . . . . . . . . . . . . . . . . iii

Moving Forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ix

ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

1 . INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 . THE PROBLEMS OF MANAGING HIGH-ACTIVITY WASTE . . . . . . . . 5

2 .1 . Origin and Description of High-Activity Waste . . . . . . . . . . . . . . . . . . . . . . . . 5

2 .2 . Properties of the Waste That Make It Difficult to Manage . . . . . . . . . . . . . . . 9

2 .3 . Permanent Disposal of High-Activity Waste . . . . . . . . . . . . . . . . . . . . . . . . . 11

2 .4 . Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2 .5 . Partitioning and Transmutation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3 . CONTRIBUTIONS FROM THE YUCCA MOUNTAIN PROGRAM . . . . 17

3 .1 . Materials and Environments of 

 the Engineered Barrier System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3 .2 . Source-Term Quantification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3 .3 . Characterizing and Modeling the Natural System . . . . . . . . . . . . . . . . . . . . 29

3 .4 . Engineering and Prototyping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3 .5 . Integrated Total Waste-Management System . . . . . . . . . . . . . . . . . . . . . . . . 43

3 .6 . Performance Assessment and Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

CONTENTS
xii Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes

4 . CONTRIBUTIONS FROM THE EXPERIENCES 

 OF OTHER PROGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

4 .1 . Learning from Other Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

4 .2 . Deep Geologic Repository Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

4 .3 . Technical Factors and Approaches Common to 

 Many High-Activity Waste Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4 .4 . Contribution of Multinational Agencies to 

 Repository Development Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

5 . MOVING FORWARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Ensuring the Availability and Accessibility of the 

Current Technical Experience Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Site Selection and Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

The Waste Form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Developing Integrated Organizational and Project Plans . . . . . . . . . . . . . . . . . . 73

Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

6 . REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

APPENDIX A-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Evolution of the Conceptual Description of Atmospheric 

Dust and the Waste-Package Corrosion Environment . . . . . . . . . . . . . . . . . . . . . 87

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

APPENDIX A-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Iterative Nature of Geologic Site Investigation and Characterization . . . . . . . . . 91

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

APPENDIX A-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Thermal Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

APPENDIX A-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Summary of the October 2010 U .S . Nuclear Waste Technical 

Review Board Meeting on Lessons Learned from 

High-Activity Waste Management and Disposal Efforts in the 

United States and Other Countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Panel I: View from Within The Yucca Mountain Project . . . . . . . . . . . . . . . . . . . . 99

Panel II: Views of Affected State and Local Governments . . . . . . . . . . . . . . . . . 101

Panel III: View from Other Countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Public Comment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
ABG Advisory Bodies to Government 

BWR boiling-water reactor 

CSDP Cask System Development Program 

DOE United States Department of Energy 

DOE-NE DOE Office of Nuclear Energy 

EBS engineered barrier system 

FSC Forum on Stakeholder Confidence 

GRS Gesellschaft für Anlagen- und Reaktorsicherheit mbH 

HLW high-level radioactive waste 

IAEA International Atomic Energy Agency 

IGSC Integration Group for the Safety Case 

INL Idaho National Laboratory 

LA license application 

LLNL Lawrence Livermore National Laboratory 

LSN Licensing Support Network (www.lsnnet.gov) 

LTCTF Long-Term Corrosion Test Facility 

LWR light-water reactor 

M&O management and operating (contractor) 

Mg megagram (1 metric ton or 1 tonne) 

MOX mixed oxide (fuel) 

MPC multipurpose canister 

NEA Nuclear Energy Agency 

NEPA National Environmental Policy Act 

NRC National Research Council 

NWTRB U.S. Nuclear Waste Technical Review Board 

OCRWM DOE Office of Civilian Radioactive Waste Management 

ORNL Oak Ridge National Laboratory 

PMA performance margin analysis 

PRA probabilistic risk assessment 

PWR pressurized-water reactor 

SKB Svensk Kärnbränslehantering AB 

SNCNW Swedish National Council for Nuclear Waste 

ABBrEviATiONS
 

Abbreviations xiii 
SNF spent nuclear fuel 

SNL Sandia National Laboratories 

SRS Savannah River Site 

TAD transport-aging-disposal (canister) 

TECDOC technical document 

TMRB Technical Management Review Board 

TSPA Total System Performance Assessment 

URL Underground Research Laboratory 

USGS United States Geological Survey 

WIPP Waste Isolation Pilot Plant 

YM Yucca Mountain 

xiv Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
1. iNTrODUCTiON
 

In February 2010, the Administration proposed to eliminate funding for the Yucca 

Mountain program in fiscal year 2011. Explaining this decision, the Administration stated 

that it “...has determined that developing a repository at Yucca Mountain is not a workable 

option and that the Nation needs a better solution for nuclear waste disposal.” (OMB 2010: 

62). Shortly thereafter, the U.S. Department of Energy (DOE) petitioned the U.S. Nuclear 

Regulatory Commission’s Atomic Safety and Licensing Board to withdraw DOE’s application 

for a license to construct a deep geologic repository for spent nuclear fuel (SNF) and highlevel radioactive waste (HLW) at Yucca Mountain. By October 1, 2010, DOE had dismantled 

its Office of Civilian Radioactive Waste Management (OCRWM) and had merged 

OCRWM’s remaining functions under the Nuclear Waste Policy Act (NWPA) into other 

parts of DOE. Most employees of OCRWM and its contractors have transferred to other 

parts of DOE, retired, resigned, accepted employment elsewhere, or become unemployed. In 

short, the program’s corporate memory is diminishing rapidly. 

One or more geologic repositories eventually will be needed in the United States. The Board 

believes that there are technical lessons to be learned from the experience gained during the 

Yucca Mountain program and other repository programs. The lessons could be valuable if 

the United States embarks on another effort to develop a deep geologic repository. Moreover, 

many of the lessons are relevant if the Yucca Mountain program is restarted.1

 Therefore, the 

Board decided to write this report, the purpose of which is to provide a technical-experience 

and status report on a permanent solution for managing high-activity waste.2

 The report is 

based principally on the experience gained from the Yucca Mountain program. 

As of May 2011, the Yucca Mountain licensing process continues, although at a minimal 

level. Many parties have been admitted to the licensing proceedings, including DOE, the 

Nuclear Regulatory Commission, the State of Nevada, several Nevada counties, the Nuclear 

Energy Institute, and others. The Board is not a party to the proceedings. An extraordinarily 

high number of contentions, approximately 300, have been allowed into the proceedings 

by the independent judges of the Nuclear Regulatory Commission’s Atomic Safety and 

1 DOE’s petition to withdraw its application has been challenged before the Atomic Safety and Licensing 

Board and in the Court of Appeals for the District of Columbia Circuit. Congress has not determined what 

funding, if any, the program would receive for fiscal year 2012. 

2 The term “high-activity waste” refers to SNF, HLW, or both. 

Introduction 1 
Licensing Board Panel. The large majority of the contentions are technical. Besides 

applying to Yucca Mountain, the outcome of many of those contentions could have generic 

implications. Thus the Board supported (NWTRB 2009a) DOE’s plans to continue with the 

licensing process despite termination of the program (DOE 2009: 504). In 2010, however, 

DOE decided to discontinue the license application and eliminate all funding for any aspect 

of the Yucca Mountain program by October 1, 2010 (DOE 2010: 163). 

The Board was created in the 1987 amendments to the NWPA (PL 100-203) to provide 

ongoing independent expert advice to DOE and Congress on technical issues of nuclear 

waste management and to build public confidence through peer review of DOE’s 

technical activities in the nuclear waste area (Congress 1987a). The Board’s responsibilities 

are to (1) evaluate the scientific and technical validity of activities undertaken by the 

Secretary of Energy to implement the NWPA and (2) report the findings, conclusions, 

and recommendations from its evaluations to Congress, the Secretary, and the public 

semiannually. This report in many respects summarizes the Board’s work in fulfilling 

those responsibilities over the course of the last 20 years.3

 During that time, the Board 

has examined the latest technologies applicable to deep geologic disposal, transportation, 

packaging, and long-term storage of high-activity waste. It has conducted more than 130 

public meetings, and it has supplemented its technical analyses with an extensive review 

of international activities, fact-finding trips to DOE sites and National Laboratories, and 

workshops on generic topics of nuclear waste management. 

This report is organized into four chapters following this introduction. Chapter 2 

characterizes the technical issues associated with managing high-activity waste. Chapter 3 

discusses lessons learned from the Yucca Mountain program. Chapter 4 describes insights 

from waste-management programs of other countries and the waste-management research 

and coordinating activities of the International Atomic Energy Agency and the Nuclear 

Energy Agency. Chapter 5 presents the Board’s overall conclusions on scientific and 

technical issues for future geologic repository programs. 

Appendices A-1, A-2, and A-3 give additional detailed information on the waste-package 

environment, characterization of a potential repository site, and thermal management, 

respectively. Appendix A-4 contains views and comments of participants in a public “lessons 

learned” meeting that the Board held on October 26, 2010, in Dulles, Virginia. 

The Board members are listed at the front of this report. Board member disciplines 

include civil engineering, corrosion science, environmental engineering, geochemistry, 

3 All of the current Board members joined the Board in mid-2002 or later, which is after the Secretary of 

Energy’s February 14, 2002, recommendation of approval of the Yucca Mountain site to the President. 

According to Section 114 of the NWPA, that recommendation marked completion of site-characterization 

activities. Thus, this report emphasizes the licensing and engineering phases of the Yucca Mountain 

program. 

2 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
geology, hydrology, materials science and engineering, nuclear engineering, physics, 

and risk assessment. The average professional service of each member is more than 40 

years. Members were nominated by the National Academy of Sciences and appointed by 

the President on the basis of eminence in their respective fields and established records 

of distinguished service. Four members have served for more than eight years on the 

Board; six members have served for more than six years; and one member has served for 

more than four years. In addition, four Board members had extensive interactions with 

repository programs before joining the Board. No current Board member served on the 

Board during the site-characterization phase of the Yucca Mountain program, which 

ended when the President recommended the site in early 2002 and Congress ratified that 

decision later that year in a joint resolution (P.L. 107-200 July 23, 2002). Lessons learned 

during the site-characterization phase are based on Board correspondence, reports, and 

testimony from that period. 

Introduction 3 

2. ThE PrOBLEMS Of 

MANAGiNG hiGhACTiviTY WASTE 

Perceptions of and opinions on the long-term management of high-activity waste vary 

from it being the Achilles’ heel of nuclear power without a real solution to it being a trivial 

technical problem made complicated by mismanagement, inconsistent policies, or political 

decisions. As discussed in the next three chapters, experience gained over the last three 

decades from the Yucca Mountain program and other programs indicates that it is neither 

unsolvable nor trivial. 

High-activity waste can take on many chemical and physical forms. The waste form of the 

U.S. commercial nuclear power industry, by far the greatest current producer of high-activity 

waste, is spent nuclear fuel (SNF). A small amount of commercial SNF was reprocessed, and 

the resulting liquid waste was evaporated, mixed with glass-forming materials (borosilicate 

glass), melted, poured into stainless-steel canisters, cooled to solid form, and sealed, a 

process known as “vitrification.” The waste form of government-owned high-activity waste 

is much more complicated, primarily because of the diversity of SNF resulting from the 

nation’s nuclear reactor development, materials testing, nuclear research, naval propulsion, 

and weapons-production programs. The management of DOE-owned waste is complicated 

not only by the different waste forms but also because the waste at each DOE site varies as a 

result of the specific processing and storage techniques in use. 

2.1. OriGiN AND DESCriPTiON Of hiGh-ACTiviTY WASTE 

In terms of radioactivity, the largest amount of high-activity waste by far is the commercial 

nuclear power plant SNF associated with the generation of electricity. SNF is being generated 

in the United States at a rate of approximately 2,000 metric tons of heavy metal (MTHM)4 

per year and now totals about 68,000 MTHM.5 

A much smaller amount of high-activity waste is that from defense operations, much of 

which is referred to as “legacy waste.” The legacy waste is a product of the nuclear weapons 

program primarily associated with the war years (1941-1945) and the Cold War years 

(1947-1990). By far, the majority of this waste is in a liquid or sludge form as a result of 

4 A metric ton of heavy metal (MTHM) refers to metric tons of the elements uranium, plutonium, etc., initially in SNF before its irradiation. In this case, it essentially means metric tons of uranium where a metric 

ton is a unit of mass equal to 1,000 kilograms (2,205 pounds). 

5 Based on Nuclear Regulatory Commission 2010: 78 adjusted to January 2011. 

The Problems of Managing High-Activity Waste 5 
the waste stream from reprocessing the fuel and is in large underground tanks at Hanford, 

Washington, and the Savannah River Site (SRS) in South Carolina. A much smaller amount 

is at Idaho National Laboratory. It was originally in liquid form, but it was treated by heat, 

and virtually all of it now exists in a solid form, calcine. Cleanup of the Hanford and SRS 

tanks is in progress, and the intent is that the liquid and sludge wastes eventually will be 

partitioned into more manageable waste forms with the long-lived high-activity components 

vitrified for disposal in a deep geologic repository. 

The smallest amount of high-activity waste includes all other sources of high-activity waste, 

such as what comes from research and development activities, research and test reactors, 

advanced reactor development, and limited chemical processing operations. 

Because of the much larger amount of SNF compared to other wastes, it is very likely 

the waste form offering the greatest opportunity for major advancements in the overall 

management of high-activity waste. Table 1 shows the approximate amounts of SNF in 

the United States. Although recycling or partitioning and transmutation of this waste 

Table 1 

APPrOxiMATE AMOUNTS Of U.S. SPENT NUCLEAr fUEL 

(ESTiMATED ThrOUGh 2010) 

FUEL TYPE QUANTITY 

(MTHM) 

LOCATION AND TYPE OF 

STORAGE 

COMMENTS 

Commercial 51,000 Nuclear Plant Site, Pool Stored at 72 plant sites in 33 

states 

Commercial 14,000 Nuclear Plant Site, Dry Stored at >50 plant sites 

Commercial 700 GE Morris Operation, Pool May be shipped back to 

generator 

DOE Material 

Production 

2,130 Hanford, Dry Spent fuel from weapons 

production reactors 

DOE Electric 

Power 

283 Hanford, Dry 

Idaho National Laboratory, Dry 

Savannah River Site, Pool 

Commercial spent fuel shipped 

to DOE for examination and 

development 

DOE 

Experimental 

Power 

42 Idaho National Laboratory, Dry 

Savannah River Site, Pool 

Spent fuel from developmental 

reactors 

DOE Test, 

Research, and 

Education 

26 Hanford, Dry 

Idaho National Laboratory, Dry 

Savannah River Site, Pool 

Includes some spent fuel from 

foreign reactors 

DOE Defense 

Power 

25 Idaho National Laboratory, Pool 

and Dry 

Spent naval fuel 

TOTAL ~68,206 ~96% COMMERCIAL SPENT NUCLEAR FUEL 

6 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
eventually may be done on a large scale, economics, nonproliferation issues, and technical 

issues do not indicate that deployment soon is likely. Meanwhile, taking a hard look at SNF 

as the principal waste form in the near term is prudent. So, the questions are just what is 

SNF in terms of a waste form, and what problems does it present for isolation? Much of 

the information in this chapter is based on a paper prepared for the National Academy of 

Engineering (Garrick 2003), including the precursor to Table 1. 

Except for very small amounts of SNF from the Fort St. Vrain gas-cooled reactor and early 

stainless-steel-clad assemblies from light-water reactors (LWRs), U.S. commercial SNF is all 

bundles (assemblies) of zircaloy tubes filled with uranium dioxide (UO2

) pellets enriched 

in 235U before irradiation in the reactor, pressurized with helium, and closed with welded 

zircaloy end plugs. For a pressurized-water reactor (PWR), the tubes have outside diameters 

of approximately 0.4 inch and an overall length of approximately 12 feet. Some 200-plus 

tubes make up an assembly, and nearly 200 assemblies constitute the reactor core in a large 

PWR. The dimensions and fuel enrichments are different for boiling-water reactors (BWRs), 

but the materials and neutronics are similar, resulting in essentially the same requirements 

for SNF management. Figure 1 shows a typical 8.5 in. x 8.5 in. x 12 ft. PWR fuel assembly 

without its end nozzles (DOE 2010). 

SNF from LWRs contains 235U and 238U; intermediate-lived 

fission products, such as 90Sr and 137Cs; long-lived fission 

products, such as 99Tc and 129I; and relatively long-lived 

transuranic isotopes (i.e., isotopes with atomic numbers higher 

than that of uranium: 92), such as 239Pu and 243Am. The extent 

to which the fuel is irradiated (burned up) in the reactor 

determines the amount of radioactive species created. The units 

of burnup usually are taken to be the amount of thermal energy 

produced per initial unit weight of the fuel (gigawatt days per 

metric ton of heavy metal [GWd /MTHM]). Two burnups 

frequently are used in the calculations of waste inventories— 

standard historical burnup and extended burnup. For PWRs, the two burnups are 33 

and 60 GWd /MTHM, and for BWRs, the corresponding numbers are 27 and 50 (ORNL 

1992). The average burnup of SNF discharged from U.S. commercial reactors in 2001 was 

approximately 40 GWd /MTHM (DOE 2002). The trend in the nuclear power industry is 

toward progressively higher burnups, with some assemblies now attaining burnups of 60 

GWd /MTHM (Gauld et al. 2011). 

There are four sources of radioactivity in SNF—actinides,6

 fission products, spontaneous 

fission, and materials made radioactive by neutron activation. In LWRs, the UO2

 pellets 

6 Actinides are elements having an atomic number from 89 to 103, inclusive, and are all radioactive. 

Figure 1: PWR Fuel Assembly 

The Problems of Managing High-Activity Waste 7 
start out containing only 235U and 238U. After a significant runtime at power, neutron-gamma 

reactions and subsequent decays will produce 51 actinides. The fissioning of uranium results 

in 200 to 300 fission products, which dominate the short-term decay heat of SNF.7

 The third 

source of SNF radioactivity consists of selected actinides that fission spontaneously; that 

is, they do not need an outside source of energy, such as an impacting neutron, to fission. 

The fourth source of radioactivity is neutron activation products due to the absorption of 

neutrons by cladding and other structures inside the reactor. 

Thus, when nuclear fuel has completed its multiyear sojourn in a reactor, there are dozens 

of actinides and hundreds of fission products, most of which are radioactive, that were not 

part of the fuel originally. In addition, there are some activation products in the structural 

material, cladding, and fuel matrix. Fortunately, most radionuclides become unimportant 

for disposal because of their minor quantities, short half-lives, or minor biological 

consequences. Basically, three categories of radioactive species dominate considerations 

for geologic repository design. The first consists of intermediate-lived radionuclides, 

especially 90Sr and 137Cs. Although they are not considered a postclosure repository health 

risk because of their relatively short half-lives (28.8 years and 30.1 years, respectively), 

they are the dominant contributors to the heat released by spent fuel during the first 

hundred years after irradiation. They also are a major part of the radiation source to be 

considered in handling, storage, and transportation operations before disposal. Decayheat load can be a major issue in repository design if there are limits on the size of the 

repository. 

The second category of important radioactive species for repository design comprises 

certain long-lived fission products, such as 14C, 36Cl, 79Se, 99Tc, 126Sn, and 129I. These 

radionuclides have half-lives of thousands of years or more and are in some abundance in 

the inventory. In general, they have significant solubility under many circumstances and 

tend not to be greatly retarded by geochemical effects and thus able to migrate relatively 

quickly on release to groundwater. 

The third category is from the actinide group of radioactive species. Although these isotopes 

are not very soluble and tend to be significantly retarded by geochemical effects during 

migration (237Np can be an exception), they have very long half-lives and, as a class, are 

significantly more radiotoxic than fission and activation products. 

7 For a spent PWR fuel assembly with an initial enrichment of 3.72% U-235 and a burnup of 40 GWd/ 

MTHM, the heat load decreases from 10,600 watts per MTHM 1 year after discharge to 16 watts per 

MTHM in 10,000 years. The values for a BWR spent fuel assembly (3.21% initial enrichment and 35 GWd/ 

MTHM) are 9,200 and 15, respectively. Source: Program RADDB (DOE 1987). 

8 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
2.2. PrOPErTiES Of ThE WASTE ThAT 

MAKE iT DiffiCULT TO MANAGE 

The goal of all high-activity waste-management programs is to isolate the radionuclides 

from biological systems, especially human beings. That sounds pretty straightforward, 

but there are complications. Two complications are that the isolation of some waste forms 

has to be for hundreds of thousands of years and that some radionuclides exist in several 

phases (gas, liquid, or solid) and have various pathways (ingestion, inhalation, external 

radiation) for spreading their radiotoxicity. The very long half-lives present major challenges 

to demonstrating that the waste is not released in unacceptable quantities. Another 

complication is that the waste may contain 200 to 300 different radioactive species, all of 

which have different chemical properties, physical properties, or half-lives. In general, 

the risk posed by a radioactive species depends on its half-life, geochemical mobility, and 

radiotoxicity. 

The good news is that some of these properties work in favor of isolation. Most 

radionuclides become unimportant quickly because of minor quantities, short half-lives, 

and minor biological consequences. Thus, although freshly discharged fuel from a nuclear 

reactor may have some 300 radioactive species that were not in the fuel when it was loaded 

into the reactor, by the time it is put in isolation, such as in a geologic repository, only a 

small fraction of the radioactive species represents a challenge to complete containment and 

isolation. Even that small fraction dwindles to no more than a couple of dozen long-lived 

radionuclides in several thousand years. Because isolating those radionuclides from the 

environment is the challenge, they are the focus of this discussion. 

Geochemical mobility is a principal issue of geologic disposal. For example, if all of the 

radionuclides were insoluble, there would be little problem, because the primary transporter 

of radionuclides in a geologic repository is water. Insoluble species would not be transported 

in flowing water through the geologic medium, and containment would be achieved, 

barring something like transport in colloidal form (i.e., transport as a suspension of fine, 

dispersed particles that do not settle out) or an igneous or other cataclysmic event. However, 

no species is truly insoluble; virtually all species are soluble in any molecular form, and the 

maximum aqueous concentration attainable for a given solid is called the “solubility limit.” 

Solubility limits for some species can be high, such as for nitrates, and for the same species 

be low when in an oxide or hydrated oxide form. Plutonium is an example. Some plutonium 

compounds have relatively low solubility values—oxides and hydrated oxides are examples. 

Assuming that the radionuclides in waste forms that have been disposed of in a geologic 

repository are completely available, the rate of radionuclide mobilization at steady state is the 

product of the groundwater-flow rate through the waste forms and solubility. 

The Problems of Managing High-Activity Waste 9 
Various processes affect the geochemical mobility of radionuclides. During groundwater 

flow in a rock matrix or fractures, transport rates for reactive solutes often are slower than 

the average groundwater-flow rate. This is because of several active phenomena, including 

diffusion of solutes into stagnant pore spaces, sorption onto fixed mineral surfaces or 

slow-moving colloids, and chemical processes, such as precipitation and replacement 

reactions with existing rock minerals. On the other hand, other processes could enhance 

radionuclide transport (e.g., low-solubility radionuclides, such as plutonium, that attach 

to mobile colloids). Many of these phenomena are difficult to quantify and depend on the 

variety of rock types through which groundwater flows and the chemical compositions of 

the groundwater. 

A few radionuclides—for example the fission products 99Tc and 129I—have three properties 

that makes their isolation difficult: very long half-lives, considerable inventory in the 

waste, and high solubility limits under geologic conditions.8

 The result is that these two 

radionuclides are for the most part able to migrate unimpeded in groundwater flow, 

assuming that no significant retardation processes operate. 

Actinides also present isolation difficulties. The important actinides from the standpoint 

of nuclear waste management are uranium, plutonium, neptunium, and americium. 

Actinides and their decay products account for much of the radiotoxicity of nuclear waste 

after the first 500 years of disposal. See Figure 2 (ORNL 

1995; used with permission). Although plutonium species 

generally exhibit relatively low solubilities in groundwater 

and neptunium is sparingly soluble, isotopes of plutonium 

and neptunium nevertheless represent a major part of the risk 

after several hundred years for oxidizing media. Actinides 

are responsible for the longer-term heat generation in the 

repository—particularly 238Pu, 239Pu, 240Pu, and 241Am. 237Np is 

an important daughter product of 241Am.

Although Figure 2 is useful for understanding relative risks 

of various radioisotopes in a generic sense, it is not repository 

specific because it does not take solubility limits or retardation 

(e.g., by adsorption) into account. The performance assessment 

results of the Yucca Mountain repository program illustrate 

how actinides and the fission products 99Tc and 129I can affect 

long-term risk (DOE 2009). At 10,000 years, the principal 

9

contributors to the risk are 99Tc, 14C, 239Pu, and 129I. At 1,000,000 

8 The solubility of 99Tc is low under strongly reducing conditions.
 

9 Note that the curve marked 226Ra and 230Th represents the sum of the ingestion toxicities of these two 


radioisotopes.
 

Figure 2. Toxicity from Ingestion as a Function of Decay Time 

for a Number of Nuclides in Spent LWR Fuel 9 

10 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
years, the risk is dominated by 226Ra, 242Pu, 237Np, and 129I. Although these radionuclides were 

calculated to be the principal contributors to the radiation dose, the implication is not that the 

calculated radiation doses were high; they were not. In fact, the calculated dose levels were 

extremely low and were well below the regulatory standard. 

Finally, on a more general level of why managing high-activity waste is such a challenge, 

especially in the United States, considering the waste inventory is important. An often 

overlooked technical issue facing the United States but not most other countries is the socalled legacy waste, which the United States has in much greater quantity and diversity than 

do most other countries with nuclear programs. U.S. legacy wastes are in a wide variety of 

forms and in some cases, such as much of the liquid wastes, are difficult to recover from 

storage and convert to suitable solid forms for permanent disposal. 

The characteristics and integrity of the waste form determine the burden on the balance of 

the engineered barrier system and on the natural system to contain the waste or to hold it in 

place until it essentially has decayed to acceptable radiation levels. With its wide variety of 

waste forms, the United States needs to seek a single disposal system that can accommodate 

them, process or package (both of which may be extensive and expensive) the wastes into 

more or less standard forms for disposal, or develop separate repositories for classes of 

waste forms, e.g., deep boreholes for vitrified waste and a deep geologic repository for spent 

fuel. Waste-form characteristics and inventories should be reevaluated, and the issue of the 

appropriate disposal method for each waste form should be addressed. The one-size-fitsall approach used by the Yucca Mountain program may or may not be the best approach. 

Termination of the Yucca Mountain program means that previous decisions on multiple 

repositories, waste processing and packaging, and repositories dedicated to classes of wastes 

will have to be made anew. 

2.3. PErMANENT DiSPOSAL Of hiGh-ACTiviTY WASTE 

Only two alternatives exist for the permanent disposal of high-activity waste: isolation and 

waste destruction. A third alternative, dilution, is not considered acceptable for high-activity 

wastes. Destruction alone is not a total solution, because not all the radionuclides can be 

destroyed. Preparation of the waste for destruction requires extensive processing to separate 

(partition) selected radionuclides from spent fuel and fabricate them into new fuel or targets 

for destruction. This then is followed with the actual destruction process (transmutation), 

either in dual-purpose nuclear reactors (power producers and waste burners) or in specialpurpose accelerators. All of these operations, the separation plants, and the special-purpose 

reactors and accelerators generate their own waste streams. Reprocessing spent fuel, a much 

discussed form of partitioning, is being reexamined for recovering unused uranium and 

plutonium for their energy value as well as for reducing the radiotoxicity and volume of 

waste requiring isolation. 

The Problems of Managing High-Activity Waste 11 
As discussed later, partitioning, including recycling of SNF, and transmutation are being 

challenged on their technical and economic practicality. Although many technical and 

economic obstacles to the large-scale use of partitioning and transmutation in high-activity 

waste management remain, the option of isolating high-activity waste in deep geologic 

repositories either in vitrified form or as SNF appears close to being achieved. In fact, deep 

geologic disposal has gained international consensus as the preferred option for managing 

high-activity waste. Interest in geologic disposal has existed for many decades. For example, 

the National Academy of Sciences, in one of the first reports on radioactive waste, concluded 

that geologic disposal of solidified high-activity wastes is feasible and recommended 

investigating disposal in salt formations (NRC 1957). In addition to salt, other geologic 

media, including clay, granite, basalt, and tuff, have been investigated as candidate 

environments for isolating high-activity waste. In addition, engineered barriers have come 

into focus as being an important part of the isolation strategy because they can provide long 

delays before radionuclides enter the natural system. 

2.4. iSOLATiON 

The goal of geologic disposal of high-activity radioactive waste is to protect public health 

and safety and the environment by isolating the waste. A key issue in the performance of 

a geologic repository is estimating the time and rates of release of the dose-contributing 

radionuclides from the emplaced engineered barrier system (EBS) to the natural system 

of the repository. This usually is referred to as the “source term.” In general, the longer the 

waste remains in the EBS, the lower hazard any waste that eventually escapes will present. A 

well-designed EBS should delay mobilization of the waste and release radionuclides over an 

extended period. 

Analyzing the performance of a geologic repository involves quantifying the source term 

and assessing how well the natural system isolates the radionuclides delivered to it by the 

source term. The extraordinarily long time scale, a million years for Yucca Mountain 

and some other countries (NWTRB 2009b: 9), makes the problem daunting and 

uniquely challenging. 

As further described in chapter 4, experience to date clearly shows major differences in 

the approach to engineered barriers because they are affected by differences in isolation 

strategies. For example, France and Germany are investigating clay and salt sites, 

respectively, and plan on using minimal barriers in addition to the natural system. On the 

other hand, the proposed repositories of Sweden (granite), Finland (crystalline rock10), 

10 Although both the proposed Finnish and Swedish repositories would be located approximately 400-600 

m deep in the crystalline bedrock of the Baltic Shield, the geologic media of the two repositories are not 

identical. The nature of the Swedish repository rock is granitic; the Finnish repository rock is a mixture of 

granitoids, gneisses, and migmatites. 

12 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
and the United States (tuff) all depend on the geology providing appropriate environments 

for their respective robust EBSs in addition to the protection provided by the natural 

system. The United States, which once seemed well ahead of the repository programs of 

other countries, is now behind at least Finland, France, and Sweden in terms of projected 

repository opening dates. However, the United States has an abundance of various 

geologic media and may well learn from the repository-development experiences of other 

countries as well as its own experience with Yucca Mountain and the Waste Isolation Pilot 

Plant (WIPP), a deep geologic repository for transuranic wastes located in salt beds in 

southeastern New Mexico. 

Transport by flow or diffusion in groundwater is the principal pathway by which 

radionuclides are expected to move from the engineered barriers into the natural system. 

Some radionuclides may become dissolved in the water or be transported as colloids or 

attached to colloids. Dispersal and transport pathways other than groundwater also must be 

considered to quantify the risk associated with a proposed high-activity waste repository. 

The risks include diffusion of radionuclides as a gas, entrainment of radionuclides in a 

volcanic eruption, and human intrusion. Yucca Mountain studies indicate that ambient 

groundwater flow generally represents the most significant pathway for radionuclide release. 

Assessing the performance of engineered barriers in a Yucca Mountain repository turned 

out to be more of a challenge than expected. Much of the challenge was describing the 

environment of the engineered barriers quantitatively, particularly during the thermal pulse, 

defined as the period when the surface of the waste package is at or above the boiling point 

of water. The duration of this period for any particular waste package in the repository 

design proposed for Yucca Mountain by DOE varied from a few tens of years to as much 

as a thousand years, depending on the location of the waste package in the repository; the 

amount, burnup, and age of the waste in the waste package; and other variables. Describing 

the environment quantitatively requires determining the range of values of the chemical 

and physical attributes in the immediate surroundings of the engineered barriers, including 

temperature, water composition, humidity, redox potential, pH, etc. The values are a 

function of time and location. 

There are many cost, performance, and uncertainty trade-offs in the design of engineered 

barriers. For example, exotic materials such as nickel alloys show great promise in resisting 

degradation but have an experience base of only several decades and are expensive. Iron 

has an experience base of many centuries and is low in cost but degrades more rapidly. In 

addition, there are the very practical problems of constructing underground in confined 

spaces and emplacing waste remotely in a high-radiation and decay-heat environment. 

The Problems of Managing High-Activity Waste 13 
Heat generation as a result of radioactive decay can complicate fundamental understanding 

of the performance of a geologic repository because the analytical models used to calculate 

performance of natural and engineered barriers may not be as reliable for temperatures 

above boiling as for lower temperatures. There are ways of dealing with the decay-heat 

or thermal-load problem, however. One way would be to do more research on analytical 

methods better suited to systems involving chemical, mechanical, thermal, and geochemical 

coupled processes at above-boiling temperatures. Other approaches would be to use 

engineering or operational adjustments, e.g., improve heat transfer in the repository or store 

the waste until a time that the heat no longer is sufficient to cause water to boil. Of course, 

the heat load often becomes a problem only because of spatial limits on the repository. 

That is, the problem of excessive heat loads can be reduced simply by using more real 

estate. Finally, the heat loads can in theory be reduced by separating the heat-generating 

radionuclides from the waste and destroying them through successive neutron reactions. 

Human intrusion, deliberate or as a result of drilling operations that inadvertently penetrate 

the repository, needs to be part of the risk assessment of a proposed geologic repository. 

Human intrusion is important because it represents a scenario for bypassing both the 

engineered barriers and the natural system. To date, modeling human intrusion has been 

considered more of a “stylized” stand-alone analysis rather than an attempt to quantify 

the actual risk of such a scenario. The performance assessments done for Yucca Mountain 

have not identified human intrusion as a significant contributor to the risk of a geologic 

repository. The reason is that the consequences tend to be localized, with very little material 

reaching the accessible environment. Nevertheless, it is an event that must be considered. 

In summary, fundamental understanding of the performance of a proposed geologic 

repository is a complex issue dependent on (1) the integrity of the engineered barriers, 

including the waste form and its physical state; (2) dissolution and mobilization mechanisms 

within the engineered barriers; (3) transport, retardation, and sequestering processes in the 

natural system; and (4) biological uptake. A fundamental understanding of the waste form is 

critical not only with respect to its physical and chemical state in a geologic environment but 

also in knowing how to complement its behavior with protective barriers, including backfills 

to create favorable geochemical conditions for maximizing containment of the waste. 

2.5. PArTiTiONiNG AND TrANSMUTATiON 

Partitioning is the process of separating long-lived and high-activity radionuclides from 

the waste to become targets for nuclear reactions, and transmutation is the process of 

bombarding the selected radionuclides with neutrons to create either stable nuclides or 

radionuclides with much shorter half-lives. If the species are fissionable in the spectrum of 

the neutron energies involved, then the reaction products may be fission products, most of 

14 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
which have shorter half-lives than the target species. The devices providing the neutrons 

are nuclear reactors of various neutron-energy spectrums or specialized accelerators. Both 

thermal and fast reactors (low-energy and high-energy neutron spectrums, respectively) can 

be transmuters, although fast reactors offer more flexibility because of their ability to fission 

the actinides directly. 

Partitioning and transmutation are considered potential means of reducing the burden 

on a geologic disposal repository by reducing the volume of the waste to be disposed of, 

the heat-generating capacity of the waste, or the time needed until the radiotoxicity of the 

waste has declined to a low-enough level. For example, because plutonium and minor11 

actinides are mainly responsible for the long-term radiotoxicity and heat generation in 

a repository, removal of these nuclides from the waste (partitioning) and then fissioning 

them (transmutation) could result in the remaining waste losing much of its otherwise 

dominating long-term radiotoxicity and heat-generation capability. The fission products 

99Tc and 129I have very long half-lives. With the right neutron spectrum, 99Tc can become 

stable 100Ru. Similarly, 129I can be transmuted to stable 130Xe. Because plutonium, uranium, 

neptunium, americium, curium, their decay products, iodine, and technetium are the cause 

of most of the mid-term and long-term risk of the proposed Yucca Mountain repository, 

their elimination could make designing a repository much simpler. 

So, why not go full speed ahead on an aggressive partitioning and transmutation program, 

especially because such destruction methods can be applied to widely different fuel-cycle 

strategies? The answer is that in time that may happen, but probably not unless and until 

fast reactors become more economic and reliable, and even then, only if nuclear power 

becomes a major source of energy over other alternatives under development. Although 

partitioning and transmutation are theoretically possible, there are many practical problems, 

the solutions to which are still very much a challenge. Also important is that no amount of 

partitioning and transmutation eliminates the need for deep geologic disposal, because all 

fuel cycles generate long-lived radioactive wastes that cannot be practically destroyed. 

The reasons for not being able to deploy waste-destruction schemes in the near future are 

many. One overarching issue is developing enough facilities to make a significant difference. 

Quoting from a National Research Council study (NRC 1996), “...to have a significant 

benefit for waste disposal, an entire S&T (separation and transmutation) system consisting 

of many facilities would have to operate in a highly integrated manner from several decades 

to hundreds of years. The deployment of an S&T system that is extensive enough to have a 

significant effect on the disposition of the accumulated LWR spent fuel would require many 

tens to hundreds of billions of dollars and take several decades to implement.” Even if the 

facilities are available, many decades would be needed on the basis of current technology 

11 The minor actinides are neptunium, americium, curium, berkelium, and californium. The major 

actinides are plutonium and uranium. 

The Problems of Managing High-Activity Waste 15 
to destroy even a fraction of the long-lived radionuclides already in the inventory. Most of 

the long-lived radionuclides would have to be recycled several times through a reactor or an 

accelerator to be destroyed to a significant degree. The facilities would produce nuclear waste 

streams of their own, many of which have yet to be well characterized. 

The foregoing does not mean that there should not be an ongoing research and development 

program on partitioning and transmutation or that there are not opportunities for 

selectively implementing partitioning and transmutation in phases. In fact, partitioning and 

transmutation are ongoing at the international level: separating plutonium from commercial 

fuel by reprocessing and recycling the plutonium as mixed oxide fuel (MOX). Reprocessing 

commercial SNF is practiced in France, Russia, Japan, the United Kingdom, and in the 

past in the United States. The United States stopped reprocessing commercial SNF in 1972, 

when the Nuclear Fuel Services plant in West Valley, New York, shut down to perform plant 

upgrades. For regulatory, economic, and other reasons, the plant did not resume operating. 

Reprocessing is being evaluated for its costs and benefits. The main concerns include 

economics and the effect of reprocessing on nuclear wastes. The price of the products of 

reprocessing, uranium and plutonium, is determined by the price of natural uranium. The 

current price of natural uranium is higher than the long-term average but considerably 

lower than recent peaks. Uranium resources appear ample at least until the end of 

the century (MIT 2010, NWTRB 2010). Compared with the once-through fuel cycle, 

reprocessing reduces somewhat the amount, radiotoxicity, and heat load of the high-activity 

waste requiring disposal. However, the isotopic quality of the uranium and plutonium 

recovered decreases each time that spent fuel is recycled, which makes multiple recycling 

increasingly impractical. 

16 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
3. CONTriBUTiONS frOM 

ThE YUCCA MOUNTAiN 

PrOGrAM 

The history of Yucca Mountain as a potential repository site spanned more than 30 years, 

beginning officially in 1977, when Yucca Mountain was selected as one of several candidates 

to be investigated for the nation’s first deep geologic repository for disposal of high-activity 

waste (DOE 1986a). In 1987, Congress directed DOE to study only Yucca Mountain 

(Congress 1987b). Site characterization occupied the 1977–2000 period for the most part, 

while the last decade consisted mostly of license application activities and related project 

engineering. Site characterization consisted mostly of scientific investigations of the geology 

and of the materials that would constitute the engineered barrier system. There was some 

engineering effort during site characterization, but it was of a very preliminary nature. 

Scientific activities decreased during the 2000–2010 period. The emphasis for science was 

consolidating information obtained and using it in computer models to demonstrate the 

safety of a Yucca Mountain repository. Little new data were gathered during the last 10 years, 

and much of the data came from ongoing existing experiments. Yucca Mountain graduated 

from a concept to a project at approximately the turn of the century, albeit a very large, very 

expensive, first-of-a-kind project. 

The site-characterization phase of the Yucca Mountain program officially ended in 2002: 

Secretary of Energy Spencer Abraham recommended the site to President George W. Bush 

in February (Abraham 2002), and the President recommended the site to Congress, also in 

February (Bush 2002). In July 2002, acting on the President’s recommendation, Congress 

gave DOE the authority to prepare and submit a license application for constructing a 

repository at Yucca Mountain (Congress 2002). DOE submitted the license application in 

June 2008, and the Nuclear Regulatory Commission accepted it for review three months 

later (DOE 2008a; Nuclear Regulatory Commission 2008). DOE requested permission to 

withdraw the application in March 2010, and the Nuclear Regulatory Commission staff 

performing the review were directed in October 2010 to make the transition to an orderly 

close-out (Irwin et al. 2010a; Jaczko 2010). 

Although site characterization ended officially in 2002, DOE began steps to facilitate the 

transition in program emphasis from site characterization to licensing and engineering 

several years earlier. For example, in 1999, DOE decided to recompete its contract for a 

management and operating contractor (Barrett 1999) with a new contract focusing on 

Contributions from the Yucca Mountain Program 17 
a licensing and design work scope (Itkin 2000). The new management and operating 

contractor, a team led by Bechtel SAIC Company, LLC, replaced a contractor team led by 

TRW Environmental Safety Systems, Inc., in late 2000. 

In this chapter, the Board discusses contributions to future repository programs from both 

the site-characterization phase and the license-application phase of the Yucca Mountain 

program, including its related project engineering. 

3.1. MATEriALS AND ENvirONMENTS Of 

ThE ENGiNEErED BArriEr SYSTEM 

Robust Waste Package Design 

DOE’s Office of Civilian Radioactive Waste Management was investigating three potential 

repository sites in the mid-1980s: a bedded salt site in Deaf Smith County, Texas; a basalt site 

at Hanford, Washington; and a tuff site at Yucca Mountain in Nevada. Because the emphasis 

was on obtaining geologic data for comparing the three sites, relatively little attention was 

paid to the waste package that could be used at any of the candidate sites. 

The original conceptual EBS design for the Yucca Mountain site called for only a thinwalled stainless-steel waste package that would have a limited life. Conceptual designs of 

waste packages for the other two sites were similarly short-lived. In fact, Nuclear Regulatory 

Commission regulations in effect for repositories at the time12 appeared to limit the credit 

that could be taken for the waste packages to no more than 1,000 years—the approximate 

maximum duration of the thermal pulse.13 

In July 1990,14 the Nuclear Regulatory Commission clarified that the regulations did allow 

robust waste packages, i.e., waste packages that could last longer than 1,000 years. In its 

November 1990 report to Congress and the Secretary of Energy, the Board recommended 

that DOE adopt a long-lived, robust EBS and that DOE conduct a workshop on the “... 

practicality, advantages, and disadvantages of a robust, extended-life EBS” (NWTRB 1990). 

Part of the Board’s reasoning underlying the recommendation was that the fabrication and 

materials of construction of the waste package would be controllable and therefore the 

behavior of the waste packages over time would be predictable. DOE held a workshop on 

robust engineered barriers in Denver, Colorado, in June 1991, and adopted a robust waste 

package design and discarded the thin-wall design by the end of the following year. The 

12 See 10 CFR 60(a)(1)(ii)(A).
 

13The thermal pulse is the period when waste package surface temperatures are substantially above ambient 


at repository depth. For Yucca Mountain, the thermal pulse begins when the repository is closed and lasts 


until waste package surface temperatures drop below 100°C. The duration of the thermal pulse for a waste 


package depends on the age of the high-activity waste in the package, the position of the package in the 


repository, and many other variables. For Yucca Mountain, the thermal pulse for some of the packages in 


the central area of the repository could last as long as 1,000 years.
 

14 Nuclear Regulatory Commission Staff Position Paper 60-001; July 27 1990.
 

18 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
Board believes that the reasoning for its advocacy of a robust waste package applies to many 

if not all future repositories, and thus the Board recommends that future U.S. repository 

programs consider robust waste packages, regardless of the site chosen. 

The robust waste package design adopted by DOE in 1992 had two walls: a moderately thick 

inner wall of corrosion-resistant alloy, e.g., 1 in. of Alloy 825; and a thick outer wall of either 

a corrosion-allowance material, e.g., 3 in. of carbon steel, or another corrosion-resistant 

material, e.g., 3 in. of a cupronickel alloy. The design adopted in 1992 went through changes 

in materials of construction, wall thicknesses, and other variables before the final design 

used in the license application was arrived at in early 1999. The final design has a 2-in. inner 

wall of 316 stainless steel and a 1-in. outer wall of Alloy 22 (a corrosion-resistant nickel alloy; 

see Figure 3). The waste package is cylindrical and has outer dimensions approximately 6 

ft. in diameter and 15 ft. 

in length. It can hold 21 

PWR assemblies or 44 

BWR assemblies. A waste 

package of the size adopted 

by the Yucca Mountain 

program, although large 

enough for a transportaging-disposal (TAD) 

canister, would not be able 

to accommodate canisters 

currently used in drystorage systems.15 Future 

repository developers should 

ensure that repository 

designs, waste package sizes, 

and the sizes of canisters 

used in dry-storage systems 

are compatible, if feasible. 

The Roles of the Engineered Barrier System and the Natural System 

The defense-in-depth principle—using multiple independent, redundant barriers to 

achieve a safety goal—is a hallmark of complex systems, whether they are software, space 

exploration, security, nuclear power plants, or geologic repositories. The EBS proposed for 

the Yucca Mountain repository has many barriers including, more-or-less from inside out, 

the following: 

15TAD canisters are discussed in section 3.5. The maximum weight of a waste package containing 21 PWR 

assemblies in a TAD canister is approximately 74 metric tons. 

Fig. 3 Final Robust Waste Package Design (Russell 2000) 

Contributions from the Yucca Mountain Program 19 
•	 the solid high-activity waste itself, which degrades and releases radionuclide slowly

when exposed to water 

•	 the cladding surrounding SNF or the canister containing vitrified HLW

•	 the stainless-steel TAD canister for commercial SNF

•	 the stainless-steel inner vessel of the waste package

•	 the Alloy-22 outer vessel of the waste package

•	 corrosion products formed if water penetrates the waste package and which can adsorb

radionuclides and form a barrier to water flow 

•	 aggregate and corrosion products in the EBS outside of the waste package, which also

absorb radionuclides 

•	 the titanium drip shield.

The natural system also has many barriers, including the following: 

•	 slow average flow rate in the unsaturated rock zone between the repository and the

water table 

•	 radionuclide-adsorbing zeolites below the repository

•	 slow flow rate in the saturated zone

•	 a long distance (18 km) in the saturated zone from below the repository to the

accessible environment. 

The importance of individual barriers varies. The difficulty of characterizing and modeling 

individual barriers also varies. DOE did not take credit for some barriers because of their 

relative unimportance or difficulty characterizing and modeling them: e.g., SNF cladding 

and zeolites in the unsaturated zone beneath the repository. 

Examination of the performance assessment and environmental assessment documents 

submitted as part of the license application and of recent presentations by DOE and its 

contractors at Board meetings shows the relative importance of various barriers (SNL 2008a; 

NWTRB 2008). Although the unsaturated zone beneath the repository and the saturated 

zone extending from below the repository to the accessible environment are formidable 

barriers, the drip shield and the waste package are much more important. That is, they are 

predicted to delay the release of radionuclides for much longer times. 

Examinations of the documents and presentations also show the relationship between 

the EBS and the natural system: Although the natural system contains several important 

20 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
barriers, its principal role at Yucca Mountain is to provide a stable, predictable, and 

relatively benign “home” in which the EBS can delay any radionuclide release for many 

tens of thousands of years and, when releases finally do occur, to ensure that they occur 

very slowly.16 A lesson to be learned is that engineered barriers have the potential to be used 

to overcome weaknesses in natural barriers. The respective roles of engineered barriers and 

natural barriers at other sites or in other geologic media can be different, as discussed in 

subsection 4.2 of chapter 4. 

Predictability of the Rate of General Corrosion for 

Long Periods in Known Environments 

Stainless steel and nickel-based alloys depend on a thin passive layer of oxides and 

oxyhydroxides for protection from corrosion. The layer blocks or severely retards 

the ability of oxygen or water to penetrate to and react with the alloy. If liquid water 

is present, general corrosion (also known as “uniform corrosion”) always occurs in 

oxidizing environments, even if conditions are benign (e.g., room temperature, neutral 

pH, low concentrations of dissolved salts in the water). The rate of general corrosion may 

be extremely low in such conditions, however. Localized corrosion or stress corrosion 

cracking, in contrast, usually requires more-aggressive environments and other features, 

such as small occluded areas on the waste package surface, areas of high tensile stress, or 

small areas where halides concentrate. If localized corrosion or stress corrosion cracking 

occurs, it can proceed rapidly. 

Assuming that the environments to which waste packages will be exposed over time are 

known or bounded, the general-corrosion behavior of the packages over long periods 

is predictable. Before the Yucca Mountain program, little thought had been given to 

the question of whether waste packages constructed from metals or alloys protected by 

passivity could be designed to last hundreds of thousands of years. The Yucca Mountain 

program presented evidence that such waste packages could be designed, depending on 

the repository environment and the avoidance of localized corrosion or stress corrosion 

cracking. The evidence included multiyear corrosion data in environments relevant to Yucca 

Mountain and models based on accepted physical principles (SNL 2007a). This experience 

allows confidence that future repository programs may be able to take advantage of verylong-lived waste packages. 

Studies of waste package corrosion evolved in important ways as data were obtained, 

understanding of the waste package environment increased, the role of the waste package 

16 Whether DOE successfully established that the EBS could achieve its role would have been decided by 

the Nuclear Regulatory Commission during licensing. The outcome of the licensing process would have 

determined whether the engineered system could compensate for site shortcomings—an important generic 

technical lesson that was a principal reason that the Board supported continuing the licensing process 

regardless of the nation’s direction on nuclear waste disposal (NWTRB 2009a). 

Contributions from the Yucca Mountain Program 21 
changed, and the standard changed from 10,000 years to 1,000,000 years. Initially, the 

program staff appeared not to believe that liquid water (necessary for significant corrosion 

to occur) could exist at temperatures well above 100°C. Liquid water at temperatures well 

above 100°C will occur if certain combinations of common salts are in the dusts deposited 

on waste packages by ventilation air during the period following emplacement but before 

repository closure. 

If the waste package is an important long-term barrier in future repository programs, corrosion 

investigators and repository environment investigators should reexamine the Yucca Mountain 

experience, should be flexible and adaptable as new data are obtained and as requirements for 

waste package performance change, and should use care to ensure that sufficient understanding 

exists of elevated temperatures where liquid water could be present in the form of concentrated 

multicomponent brines. 

To summarize, isolation of wastes by corrosion-resistant, nickel-rich (Alloy-22) containers 

provides the principal radionuclide isolation in DOE’s quantitative performance models for 

the proposed Yucca Mountain repository. Because waste package materials and fabrication 

methods can be carefully controlled, analyzing the behavior of the waste package and 

predicting its lifetime are tractable, provided that localized corrosion and stress corrosion 

cracking can be prevented. If the waste package is also robust (thick-walled), the lifetime of 

the waste package may be extended. Although still dwarfed by the “lifetime” of the natural 

system, a waste package with a million-year-plus lifetime is very important because only 

a very few radionuclides with extremely long half-lives (e.g., 242Pu, 237Np, 129I, with halflives of 0.38 million years, 2.14 million years, and 15.7 million years, respectively) remain. 

Moreover, because temperatures can be expected to be low, 25 to 30°C, when packages do 

fail and because the natural environment will have returned to its ambient state before being 

disturbed by repository construction and decay heat, analysis of the source term may be 

simplified. Of course, no matter how carefully controlled the materials and fabrication of the 

waste package, corrosion behavior cannot be predicted accurately and confidently unless the 

environment is also known well, or at least bounded. 

Corrosion Technical Management 

Although the Yucca Mountain program never lacked highly capable corrosion scientists 

and engineers, its technical management of corrosion was at times deficient. This was 

particularly the case during the period beginning in the late 1990s and extending into 

2006. This was a period that began with the waste package being one of several engineered 

and natural barriers in a 10,000-year repository and ended with the waste package being 

arguably the most important engineered barrier in a 1,000,000-year repository. There 

were several possible reasons for the subpar corrosion management: (1) Diffusion of 

authority and responsibility for corrosion among DOE, DOE’s support contractor, DOE’s 

22 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
management and operating (M&O) contractor, and the National Laboratories performing 

corrosion-related work; (2) Lack of continuity, particularly due to retirements of key 

personnel, changes in M&O contractors, changes in reporting relationships between the 

M&O contractor and the National Laboratories, and the move to a lead laboratory; and (3) 

Inconsistency in funding for corrosion activities, which made attracting and retaining senior 

corrosion managers difficult. 

The lack of continuous strong corrosion leadership hampered the program. For example, 

in the late 1990s, it became evident that water could exist on waste package surfaces 

because of the elevation of boiling point from concentrated salt solutions (brines) formed 

by the deliquescence of salts carried into the repository in ventilation air during the 

preclosure period, a period anticipated to last at least 50 years. New corrosion tests had 

to be devised in the laboratory to address the higher-temperature conditions. Many 

of the new tests were done in concentrated solutions of pure calcium chloride (SNL 

2007a), a poor choice because pure calcium chloride solutions are unlikely to exist at 

Yucca Mountain. More likely, because the salts entrained in the ventilation air would be a 

mixture of salts, including calcium chloride, the brines resulting from their deliquescence 

would be a mixture of several salts dissolved in water. The fact that so many of the tests 

were performed in calcium chloride solutions rather than in more realistic mixed-salt 

solutions is an indicator of weak corrosion management. 

For future repository programs where corrosion is important, the Board recommends that 

strong technical corrosion management be established at the inception of investigations and 

maintained not only throughout the investigations but also throughout subsequent program 

phases, including site-suitability determination, license-application preparation and review, 

construction, operation, performance confirmation, and closure. 

Flexibility of Test Plans Because of External Changes 

DOE assigned responsibility for research on and modeling of corrosion of waste-package 

materials for a Yucca Mountain repository to Lawrence Livermore National Laboratory 

(LLNL) in the early 1980s. LLNL carried out literature studies on degradation modes of 

potential waste package materials during the 1980s, conducted limited corrosion research, 

and developed a long-range plan for corrosion research during this same period. A major 

part of the plan was the construction and operation of a long-term corrosion test facility 

(LTCTF) in which samples of candidate materials would be exposed to simulated Yucca 

Mountain environments in stirred baths for multiyear periods and their corrosion modes 

and rates determined after the exposures. The LTCTF was designed, approved, and 

constructed, and the first samples were placed in it in 1995. Eventually, more than 12,000 

samples were placed in the LTCTF. The LTCTF continued operating until 2005. 

Contributions from the Yucca Mountain Program 23 
Enactment of the Energy Policy Act of 1992 set in motion a complex and lengthy process 

that ultimately resulted in revised regulations applying to a high-level-waste repository 

located at Yucca Mountain. Taken together, two of the revisions increased the importance 

of the waste package significantly. Those revisions were (1) the performance of the 

repository as a total system was specified to be the principal measure of the merit of the 

repository (Nuclear Regulatory Commission 2001) and (2) the period for determining 

the performance of the repository was specified as a million years (EPA 2008). Before the 

revisions, there had been individual requirements for subsystems of the repository, and 

the period of performance had been limited to 10,000 years. Although the changes were 

formally adopted well after commencement of LTCTF operations, they were very much 

a matter of discussion in the mid- and late 1990s. In fact, a special panel of the National 

Research Council recommended in a 1995 publication (NRC 1995) that the period of 

performance for Yucca Mountain be until the time of peak risk17—essentially repeating a 

recommendation made for all repositories by another National Research Council panel in 

a 1983 publication (NRC 1983). 

Board members having special expertise and interest in corrosion have monitored DOE’s 

technical activities in the corrosion area closely over the years, visiting LLNL and the LTCTF 

several times, discussing corrosion matters with the Yucca Mountain program staff, and 

receiving periodic updates on corrosion-related activities at public meetings of the full 

Board or its panels. To the Board’s knowledge, the Yucca Mountain program’s corrosion 

management did not conduct a review of the LTCTF to determine whether the data it had 

produced and would produce would be adequate for the increased importance of the waste 

package. However, Sandia National Laboratories (SNL) took over corrosion responsibilities 

in late 2006 and began to scrutinize the LTCTF methodology and data. Several problems 

were found, which SNL personnel documented in “Condition Reports” (SNL 2008b; SNL 

2009). Although much of the data are still usable, some have had to be discarded, namely 

general-corrosion data based on crevice samples exposed for 5 years in the LTCTF and all 

samples exposed for 9.5 years in the LTCTF. The data based on 5-year crevice samples were 

rejected because of uncertainties about whether the samples had been cleaned completely 

before being weighed in 2002-2003 to determine weight loss. The 9.5-year data were rejected 

because of the presence of visible deposits of stirrer gear-reduction box grease on many 

of the samples. As a result of rejection of two sets of data, the case for the longevity of the 

waste packages with regard to general corrosion of Alloy 22 at below-boiling temperatures, 

although still strong, is not as strong as it once appeared to be. 

17 Within the limits of geologic stability of Yucca Mountain, which the panel judged was “on the order of one 

million years” (NRC 1995). 

24 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
The lesson learned in this case is that quality-control measures for long-term experiments need 

to be improved and established at the beginning of any research program to be assured that they 

pass the rigor of regulatory expectations. 

Whether an examination of the LTCTF procedures when the changes to the regulations 

were being discussed rather than after the regulations were formally adopted could have 

resulted in changes to the LTCTF that would allow all of its data to be used is not known. 

Nevertheless, the lesson for future repository programs is clear and applies to all technical 

areas, not just corrosion: Test plans and equipment should be reexamined when changes 

external to the program are being considered. 

Dust in Repository Ventilation Air 

The corrosion environment for waste packages is affected by dust brought in by ventilation 

air during the preclosure period. The conceptual description of the waste package corrosion 

environment due to the deposition of atmospheric dust on the metal during preclosure 

ventilation evolved considerably over the life of the Yucca Mountain program. What has 

changed is the description of the composition of the dust, what happens to the dust in a 

chemical-reaction sense, and the effect of radiolysis. That the dust layer on waste package 

surfaces is a dynamic reacting chemical system with a continual supply of reactants has 

been known for about 10 years. The dust on waste package surfaces may evolve into a brine 

by dissolving into water that drips onto the waste packages or via deliquescence by reacting 

with moisture in the air. The brine could cause or exacerbate corrosion, particularly fastacting localized corrosion. For this reason, having a complete conceptual description of the 

corrosion environment on waste package surfaces is vital. 

At least five major factors affect the evolution of the conceptualization of the corrosion 

environment on a waste package as affected by atmospheric dust, including the existence 

of calcium chloride in and on atmospheric dust; the existence of organic matter in and on 

atmospheric dust; the reaction of organic matter with nitrate in dust, depleting the nitrate 

content; radiolysis effects, including gamma radiation of halide salts producing halogen 

gases; and radiolysis of moist air producing oxides of nitrogen, specifically nitric acid. 

Examination of the details of these major factors leads to the conclusion that understanding 

of the corrosion environment as described at the time of the License Application Design 

Selection Report (CRWMS M&O 1999b) was incomplete. 

The conceptual description of the corrosion environment of a waste package determined 

in part by atmospheric dust clearly has evolved in comparison to the description of 10 

years ago. The experience gained in this evolution applies to a description of any corrosion 

environment that results from exposure to the atmosphere, especially that expected for the 

long-term dry storage of SNF on the Earth’s surface, where natural-convection cooling using 

the atmosphere is expected to be implemented. Many, possibly all, future repositories may 

Contributions from the Yucca Mountain Program 25 
have extended preclosure periods. That is, the duration of the time between emplacement 

of a waste package and closure of the repository may be measured in many decades, if not 

centuries. In some repositories, dust could be deposited on waste package surfaces during 

that period, and the composition of the deposited dust would be affected by the major 

factors mentioned above. 

The composition of dust or other deposits from the natural environment determines the 

corrosion environment during the preclosure period and influences the corrosion environment 

during the period that begins immediately after closure. Thus, studying the evolution of the 

waste package surface environment is important for any future repository. 

A more detailed analysis of the evolution of the environment on waste package surfaces due 

to dust entrained in ventilation air is in Appendix A-1. 

3.2. SOUrCE-TErM QUANTifiCATiON 

For this discussion, the source term is defined as the radionuclides released to the natural 

system from the EBS. Murphy, Garrick, and Kirstein (2009) characterized the principal 

mechanisms of radionuclide isolation or release-rate reduction at the source for the 

proposed Yucca Mountain repository to be (1) diversion of water flow around the drift; (2) 

diversion of water flow by the drip shield (see Figure 4); (3) isolation of wastes by containers; 

(4) stability of the waste form(s); and (5) sequestration of radionuclides in products of waste 

package alteration. Although studies for the Yucca Mountain program (e.g., SNL 2007b) 

made significant advances in quantifying each of these isolation mechanisms, room for 

improvement in the realism of the quantifications exists, particularly for (4), as described 

later in this section. 

Research supporting the Yucca Mountain 

program led to advances in quantitative 

understanding of groundwater flow in 

fractured hydrologically unsaturated 

rock (e.g., Flint et al. 2001a, b). This 

understanding was used to model flow 

of water around and through wasteemplacement drifts. Major advances also 

were made in modeling transient heat and 

two-phase (gas and liquid) fluid flow in 

the geologic media around heat-producing 

wastes in the proposed repository (e.g., 

Figure 4. Titanium Drip Shield Buscheck 2002, 2005). Repository design was 

26 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
modified to take advantage of thermo-hydrologic effects: for example, by adoption of lineloading thermal management (CRWMS 1999b). 

The drip shield concept is unique to Yucca Mountain. Drip shields composed of corrosionresistant titanium were incorporated in the EBS to protect waste packages from water flow 

and to prevent or retard mobilization of any radionuclides escaping from prematurely failed 

waste packages. Drip shields are predicted to make a significant contribution in quantitative 

estimates of the Yucca Mountain repository’s performance (SNL 2008a).18 

Theoretical studies of the thermodynamic stability of crystalline UO2

, experimental 

studies of the alteration rate of SNF, and studies of the oxidative alteration of natural 

uraninite deposits in environments analogous to Yucca Mountain provided converging 

lines of evidence that SNF in the Yucca Mountain environment would alter by oxidation 

in a time frame that is short in comparison to its radiological hazard (e.g., Murphy 2000). 

Performance assessments used rates of waste-form alteration based on experimental data to 

define release rates of high-solubility radionuclides from the EBS to the natural system (SNL 

2008a). Despite the fact that zircaloy is highly corrosion resistant in the Yucca Mountain 

environmental conditions likely at the time of contact of zircaloy cladding by water, no 

credit was taken for zircaloy cladding in the total system performance assessment for license 

application (TSPA-LA). 

Reaction of EBS materials, e.g., waste packages and waste forms, with gas, water, and 

rocks in the Yucca Mountain environment could produce relatively stable materials with 

the capacity to sequester some radionuclides for indefinite periods. Solubility limits of 

radionuclides were quantified for source-term evaluations for the proposed repository 

(Bernot 2007). Sequestration in the waste package, but not in the EBS outside the 

waste package, also was modeled (BSC 2005). Variability and uncertainty in near-field 

environmental conditions and particularly in the compositions and properties of solid-phase 

alteration products led to uncertainties spanning many orders of magnitude in radionuclide 

concentrations in groundwater solutions (SNL 2008a). More accurate characterization 

of coprecipitation of radionuclides in thermodynamically stable secondary solids could 

have improved quantitative estimates of repository performance (e.g., Murphy and 

Grambow 2008). The rate of diffusive transport of radionuclides through waste package 

alteration materials provides transient retardation of radionuclide migration to the natural 

environment in performance-assessment models (SNL 2008a). 

A repository developer should achieve a balance of the factors contributing to the performance 

of a permanent disposal system. For example, a key calculation of the performance of any 

repository is the fractional release rate of radionuclides from the EBS to the natural system 

18 It should be noted that the importance of the drip shield to repository performance is based on the assessment made in the total system performance assessment that was part of the license application. 

Contributions from the Yucca Mountain Program 27 
as a function of time—quantification of the source term. By “balance” is meant comparable 

confidence in the representation of the various steps of the source-term calculation. 

The drip shield and the waste package eventually will fail to the point where they allow 

water to reach the high-activity waste. Because of many conservative assumptions,19 the 

portrayal of degradation, mineralization, sorption, transport, dissolution, mobilization, 

and sequestration of the waste form or its radionuclides as a function of the changing 

environment and time in the models and analyses included in the license application and 

its supporting materials was unrealistic. The outcome of the source-term model might have 

been very different if its processes had been modeled differently. Certainly, the confidence in 

the realism of the analysis would have been different. 

The form and rate of radionuclides entering the natural system are critical to assessing 

repository performance. In particular, the form determines their behavior in the natural 

system. Transport, retardation, and sequestering need to be quantified to answer the risk 

question. There is a need to consider the possibility of different chemical and mineral forms 

of radionuclides released into the natural system and, in the spirit of risk assessment, to 

determine the likelihood of receiving different radiation-dose levels on the basis of the 

supporting evidence, while quantifying the uncertainties in the probabilities. 

The source term should be quantified and realistically assessed. A realistic assessment is 

important to a fundamental understanding of barrier performance and the radionuclide forms 

entering the natural system. 

In the proposed Yucca Mountain repository, the drip shields and the waste packages are 

very important to the assessed performance of the repository. Because of their predicted 

longevity, they delay the possibility of mobilization of the waste for many hundreds of 

thousands of years until the burden of isolating the waste shifts to the waste form, the 

interaction between radionuclides released from the waste form and corrosion products 

or other materials in the EBS, and, eventually, the natural system. Thus, quantifying the 

isolation capability of the EBS is important to obtaining greater quantification of the 

source term. The Board believes that a much more realistic assessment of the EBS— 

and therefore the source term—is possible than was provided for the proposed Yucca 

Mountain repository. 

Because the modeling and simplifying assumptions for radionuclide mobilization and 

transport in the EBS were conservative, characterization of the source term was unrealistic. 

Although a great deal of effort was expended by the Yucca Mountain program on modeling 

the source term, the effect of anthropogenic materials (e.g., the metals of the waste package, 

19 Examples of conservatisms include no corrosion resistance of the stainless-steel waste package inner vessel or the stainless-steel TAD canister; no corrosion resistance of the zircaloy cladding; no plugging of waste 

package breaches by corrosion products; and no effect due to corrosion products in the invert. 

28 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
the pallet, and the invert20) on the waste-form environment was not taken fully into account 

in TSPA-LA (BSC 2005: 6-41). 

In reality, the presence of abundant reduced material and the ability of corrosion products to 

limit the access of water and oxygen are likely to cause substantial lowering of the in-package 

reduction-oxidation potential. For example, despite strong evidence that the presence of 

large amounts of iron-based waste-package or invert materials significantly reduces the 

rate of degradation of uranium dioxide or spent fuel by making the local environment 

less oxidizing (Cui et al. 2009; Ferriss et al. 2009), the effect of these materials on the 

environment was only partially taken into account (SNL 2007b; Ap. VI). 

A critical factor in the assessment of the performance of a repository, and thus the achievement 

of an optimal design, is quantifying the source term. The Yucca Mountain program placed 

too little emphasis on research on mobilization of the waste within the EBS compared with 

degradation of the waste package. A positive lesson to be learned for future repositories is the 

potential importance of the source term and the need to understand it well. The source term 

more than anything else determines the performance requirements of the natural system. 

3.3. ChArACTEriZiNG AND MODELiNG ThE NATUrAL SYSTEM 

The Value of Underground Research at Yucca Mountain 

Determining the suitability of a site for an underground repository for radioactive waste 

requires a good understanding of the site’s geology, potential future geologic processes at 

the site, and how the site could react to excavation and the decay heat of emplaced waste. 

Among other things, an ideal site would have rock that is spatially homogeneous21 and 

without flaws, such as faults, over a volume large enough to accommodate a repository. 

However, because the underground rock is hidden from view, adequately characterizing site 

geology is a challenge. Unforeseen geologic features and conditions can greatly affect the 

cost, schedule, modeling, safety of workers, and performance of the repository. 

In 1994, the Board held a meeting to review successes and failures of various attempts to site 

and license large engineering projects, such as nuclear repositories, power plants, and dams 

(NWTRB 1994). On the basis of the meeting and subsequent analysis, the Board offered 

several insights and lessons learned that it believed would be applicable to Yucca Mountain 

(NWTRB 1995): (1) Site assessment requires a strategy that is an iterative process that 

continually looks at the relationships among data gathering, modeling, and performance 

assessment; and (2) Expect surprises in any underground site investigation. Geologic 

20The pallet (sometimes called the pedestal or the platform) is the cradle-like metal structure that supports 

the waste package in the repository. The invert is the built-up steel and backfill structure that rests on the 

floor of an emplacement drift and provides a flat surface for supporting rails and the pallet. 

21 “Homogeneous rock” refers to a body of rock that is structurally, physically, and chemically uniform in its 

spatial extent. Repository-size volumes of near-homogeneous rock are not uncommon in nature. 

Contributions from the Yucca Mountain Program 29 
surprises did appear over the years of investigation at Yucca Mountain. A few examples are 

mentioned below. The surprises affected the evolving conceptual site model and repository 

design. DOE and the Yucca Mountain program remained sufficiently flexible to incorporate 

the surprises into project knowledge and modeling, but surprises sometimes led to project 

delays. Inevitably, any investigation of future repositories will encounter its share of 

surprises, and the understanding of the geology will evolve, particularly after underground 

access is provided. An illustration of one of the surprises—how the understanding of the 

geotechnical aspects of the rocks changed once investigators were able to get underground— 

is in Appendix A-2. 

Surprises that surface and underground research at Yucca Mountain revealed include that 

some water infiltrating into the mountain moves through the unsaturated zone rapidly; 

that water composition in the unsaturated zone is heterogeneous and significantly different 

from the presumed water composition before extensive site characterization started; that 

water infiltrates at a significantly higher rate than thought when site characterization 

started; that extensive perched-water systems are present; and that there is channelized 

flow in the saturated zone. Although hydrologists never thought that the Yucca Mountain 

unsaturated zone was “dry,” print and electronic media offered references to “dry” that may 

have numbered in the thousands. The idea of minimal infiltration in an arid environment 

among many unsaturated-zone hydrologists of the 1980s (e.g., Winograd 1981) pertained 

to the alluvium. Indeed, physical and chemical evidence from around Yucca Mountain 

indicates that net infiltration through thick alluvium is very close to zero. The site chosen 

for the Yucca Mountain repository, however, was fractured tuff with minimal soil cover, 

much different from the loose, unconsolidated nature of alluvium. Thus, despite the low 

precipitation at Yucca Mountain and the runoff and evapotranspiration of much of that 

precipitation, some infiltration occurs. 

The principle of expecting surprises need not preclude successful site characterization and 

permanent high-activity waste disposal. For example, preconceived notions about the basic 

technical questions of salt creep rate, rock permeability, and water abundance at the WIPP 

site all were proven wrong once the underground exploration facility was constructed. 

Another surprise was the presence of pockets of pressurized brine near the WIPP site. 

Nevertheless, that site proves to be an acceptable one for the disposal of non-heat-generating 

transuranic waste. Reasonable engineering accommodation to site-characterization reality 

worked for WIPP, just as a robust container may well have worked for Yucca Mountain. 

Hydrogeology of the Unsaturated Zone 

The U.S. Geological Survey (USGS) suggested that disposal in the unsaturated zone would 

offer advantages in deep geologic disposal of high-activity waste, the thought being that a 

site with limited water flux downward would be a benefit to repository performance (e.g., 

30 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
Winograd 1974; Roseboom 1983). The deep water table and thick unsaturated zone at Yucca 

Mountain were thought to be indications of a very low infiltration rate and therefore a 

negligible downward flux; advective transport by water was, and still is, considered the most 

serious threat to mobilizing nuclear waste. 

Studies at Yucca Mountain advanced scientific understanding of water flow in unsaturated 

fractured rock in arid regions. In particular, mass-balance methodology has been used 

to quantify infiltration and characterize the spatial distribution of net infiltration and 

recharge (Hevesi et al. 2002). In an arid environment, infiltration is the small difference 

between precipitation and water lost by runoff and evapotranspiration. The difference 

between the “input” and “output” flow is a few percent or less and can be locally negative, so 

quantification of the difference is difficult. Despite the advancements, room for additional 

improvement remains. For example, direct measurement of evapotranspiration still needs 

further development. 

The independent development of analytical technology over the last two decades led 

to the use of microstratigraphic characterization and dating of secondary mineral 

deposits of calcite and opal in fractures and lithophysal cavities22 at Yucca Mountain. The 

microstratigraphic characterization was done at the tens of microns scale to develop a 

chronology for millimeter-thick hydrogenic deposits formed over a period of longer than 

10 million years (Paces 2004). The mechanism for the deposits is not fully understood, 

however. Percolating water increases in temperature because of the geothermal gradient 

at Yucca Mountain, leading to eventual precipitation of calcite because of its retrograde 

solubility. Silica has prograde solubility, however. Murphy (2009) suggests that evaporation 

due to the warming of descending gas could explain the apparent anomalies. 

Modeling, using computers, was used extensively for project studies. Hydrologists developed 

models accounting for runoff, evaporation, plant transpiration, the effect of capillary 

forces, and other parameters. Various hypotheses were tested in the models, leading to 

improved insights on flow in unsaturated rock. The collection of models used for hydrology 

calculations underpinning performance assessments in the license application resulted 

from a decades-long iterative process of obtaining field data, testing various hypotheses, and 

refining the models. A significant modeling advance came in the coupling of multiphase 

transport in complex geologic media: The coupling of heat and fluid mass transport with 

provision for geochemical reactions in time and space allows modeling on time scales 

appropriate for consideration of nuclear waste disposal and sets the stage for future advances 

in modeling and understanding multiphase transport in geologic media. 

22 Lithophysal cavities or lithophysae are hollow bubble-like structures of varying size found within some 

tuff. 

Contributions from the Yucca Mountain Program 31 
Characterization of future repository sites that feature significant unsaturated zones will benefit 

greatly by the understanding developed as a result of characterization of Yucca Mountain’s 

unsaturated zone. 

Hydrogeology of the Saturated Zone 

Characterization of Yucca Mountain hydrology also led to advances in understanding the 

saturated zone, including the effect of matrix diffusion on radionuclide transport. As in the 

unsaturated zone, transport in the saturated zone is through both fractured and unfractured 

porous media. Part of the saturated zone consists of tightly fractured or unfractured media, 

where matrix diffusion is the dominant mode of transport. In general, sorption is more 

important in matrix diffusion than in fracture flow because of the larger rock-surface area 

relative to the volume of water. Thus, matrix diffusion into adjacent unfractured rock can slow 

the rate of movement of radionuclides through the rock in comparison to the rate of water flow 

through fractures. Besides sorption of radionuclides onto mineral surfaces, precipitation of 

minerals as chemical conditions change along the flow path also can be important. 

Understanding Thermal Management 

In general, if the temperature of the waste package’s outer surface is in the range that water 

exists as a liquid, the higher the temperature, the more rapid the degradation (corrosion) 

of the waste package.23 Similarly, the higher the temperature of the waste form when it is 

contacted by liquid water, the more rapidly it will dissolve or radionuclides will leach from 

it. Theoretically, then, one would want to keep repository temperatures as low as possible 

for best performance. There are trade-offs, however. One strategy would be to keep the 

repository hot enough to keep water in a vapor state while the degree of hazard of the waste 

declines through radioactive decay. A disadvantage of this strategy, however, is that when 

the temperature eventually drops to the point where liquid water is possible, the duration of 

the period with high-temperature liquid water would be longer than if a low-temperature 

strategy were used. 

High-activity waste generates heat as it undergoes radioactive decay. The effect of the 

decay heat on waste-form temperatures, waste-package temperatures, and repository-rock 

temperatures close to and far from the emplaced waste is most pronounced during the 

thermal pulse. How high temperatures rise during the thermal pulse and how long they 

23The gas pressure in a Yucca Mountain repository would be essentially atmospheric (~710 mm Hg at the 

altitude of the proposed repository). The lowest waste package outer surface temperature, which would 

not be reached until many thousands of years of cooling, is ~25°C. The highest temperature at which bulk 

liquid water could exist is approximately 150°C, although there is uncertainty about this figure. At atmospheric pressure and 150°C, water would need to be in the form of a concentrated, multicomponent brine 

with significant divalent halide or nitrate content to be liquid. Minerals necessary to form such a brine may 

not be present in the rock but may be carried into the repository as part of the dust in ventilation air. If 

temperatures are so high that liquid water cannot exist, there will be no corrosion by liquid water and no 

possibility of waste-form dissolution. 

32 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
stay elevated depend on a large number of variables, including the thermal conductivity 

and degree of saturation of the rock, the design of the waste packages, the amount of waste 

in each waste package, the location of the package in the repository, how closely waste 

packages are placed to each other, the type and age of the waste at emplacement, the amount 

of ventilation before repository closure, the permeability to convective gas flow of the rock 

and drifts through the rock, and many other variables. Many of these variables are design 

variables, that is, they are at least partially under the control of the designer or operator 

of the repository. The spacing of waste packages is an example of a design variable. Other 

variables are not design variables, i.e., they cannot be controlled by the repository designer 

or operator. An example is the thermal conductivity of the rock. 

The Yucca Mountain program engineers investigated many alternatives for controlling the 

temperatures in the repository (e.g., CRWMS M&O 1999a). Independently, Nye County 

contractors investigated both similar alternatives and different alternatives consisting 

of novel ventilation schemes (Danko 1997; Danko et al. 2004). The work of the Yucca 

Mountain engineers and the Nye County contractors established that there are many 

different ways to meet thermal goals and constraints and to select from for developing a 

preferred system. Future repository system designers can learn from the Yucca Mountain 

experience. 

On the basis of the analyses of its engineers, contractors, and others, DOE management 

made the fundamental decision that the Yucca Mountain repository would be based on 

a high-temperature design (Barrett 1999). Waste package surface temperatures would 

rise rapidly to above-boiling levels within a few years after repository closure and would 

remain above boiling for 50 to 1,000 years, depending on the position of the package in 

the repository, the waste loading in the waste package, and other variables. The factors 

underlying the decision, such as cost, licenseability, data availability, uncertainty, and others, 

were discussed at a Board meeting on repository design in Beatty, Nevada (NWTRB 1999). 

The decision on repository temperature is one that future repository developers face, and it 

is a difficult one to make because it must balance the value of continued radioactive decay 

and the time to peak temperature and subsequent water ingress in the repository horizon 

upon cooldown. 

Thermal Analysis 

Data are needed to construct models of corrosion, solubility, and dissolution rates. If the 

temperature range over which liquid water would be encountered is wide, more data are 

needed to construct the models than for a narrower temperature range. Ideally, one would 

have data that cover the full range of environmental conditions (temperature, pressure, water 

composition) that waste packages and waste forms would encounter. If not, extrapolation is 

necessary. Extrapolation from the 65 to 90°C range, where the bulk of the Yucca Mountain 

Contributions from the Yucca Mountain Program 33 
program’s corrosion data exist, down to 25°C presents little risk because phenomena and 

mechanisms in this range are understood. Extrapolation up from the 65 to 90°C range, 

however, presents greater risk because possible phenomena and mechanisms are less well 

known, particularly for temperatures above 100°C and particularly when water containing 

dissolved salts is at its boiling point. Data are easiest to gather at low temperatures, and 

much data already are available in the technical literature for temperatures of 25 to 50°C. As 

temperatures increase from this level, however, corrosion, solubility, or dissolution-rate data 

become scarce. Data are particularly scarce at temperatures near or above the boiling point 

of pure water. Water can be a liquid well above the boiling point of pure water if the water is 

in the form of a concentrated brine (e.g., Hoffmann and Voigt 1996). 

Thermal-analysis models and computation tools used at Yucca Mountain improved 

considerably over the last 20 years. The tools became much more efficient, which allowed 

more detail to be included in models, which in turn led to better understanding of how 

temperature profiles could change over time. Accurate estimates of thermal conductivity 

are crucial for temperature profiles in a repository. Improved understanding of the thermal 

conductivity of wet and dry lithophysal tuff (both bulk rock and crushed tuff) resulted from 

the improved computational tools, as did improved understanding of the transport of heat 

and mass in the waste-package environment. One of the Board’s contributions to the rapid 

and efficient computation of repository temperatures is described in detail in Appendix A-3. 

Natural Analog Studies 

Studies of natural analogs, particularly the Peña Blanca uranium ore deposit in northern 

Mexico, contributed to a better understanding of the long-term processes that are relevant 

to Yucca Mountain and of the long-term stability of minerals in arid regions, particularly 

the uranyl minerals. The studies contributed to a more fundamental understanding of 

climatic, geologic, and hydrologic processes that could affect repository performance in 

unsaturated zones; this applies to nuclear wastes as well as to other wastes (which are much 

more voluminous, and many of which have “infinite” half-lives). A particularly valuable 

result of natural analog studies for Yucca Mountain was demonstration of converging lines 

of evidence with respect to the geochemical evolution of the repository when compared with 

Yucca Mountain site characterization and associated experimental studies (e.g., Murphy 

2000). Other examples of natural analogs include the underground cities of Cappodocia, 

Turkey, and Egyptian tombs, which show that capillary barriers can persist over long time 

periods. Although such examples are largely anecdotal, they lend credence to claims of a 

capillary-barrier effect in the drifts at Yucca Mountain. Natural analogs proved invaluable 

for the Yucca Mountain program and may well be so for future repository programs. Natural 

analogs should be identified and studies on them initiated early in the site-characterization 

programs of future geologic repositories. 

34 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
The USGS recently published an excellent compendium of natural analogs (Simmons and 

Stuckless 2010). Although focused on analogs relevant to repositories in unsaturated rock, 

the compendium should be useful for any future repository program. Natural analogs can be 

tools for demonstrating why scientists believe their predictions. 

Solubilities of Uranyl and Neptunyl Minerals 

Experimental and theoretical work related to site characterization advanced understanding 

of the thermodynamic properties of uranyl minerals and the trace solubility of neptunyl 

in these phases (e.g., Murphy and Grambow 2008). As with many aspects of the Yucca 

Mountain natural system, additional work would improve understanding. SNL (2007c) 

states that evidence for incorporating neptunium into uranyl structures has been 

investigated only for some uranium(VI) corrosion products, the nature of the neptunium 

association with uranyl solids has not been unambiguously determined, and the effect of 

such association on dissolved concentrations of neptunium, particularly in the long term, 

has not been addressed experimentally. SNL also proposes a large number of experiments to 

obtain the following quantitative data about potentially relevant neptunium-bearing solids: 

(1) solubilities and thermodynamic stabilities in water chemistries expected in a repository; 

(2) equilibrium partitioning of neptunium between relevant solids and aqueous solutions as 

a function of solution chemistry, and possibly as a function of solid chemistry as well; and 

(3) precipitation and dissolution rates for all relevant neptunium-bearing solids. Because 

uranium, neptunium, or uranium-neptunium secondary minerals may be major contributors 

to long-term dose in future repositories, the continued study of their solubilities is warranted. 

Seismic and Volcanic Considerations 

The Yucca Mountain program contributed to how to use mapping and other studies for 

locating faults and evidence of past volcanic activity in the vicinity of potential disposal 

locations. The location, timing, and amount of movement on these faults and periods of 

volcanism were characterized as part of the hazard analysis. A major contribution was 

made to the process of expert elicitation as a method of developing a more fundamental 

understanding of phenomena such as seismic and volcanic risks and as defensible input 

to calculating the risk of seismic events of varying severities and volcanic eruptions in 

confined and unconfined spaces. A diagnostic science was developed by using precarious 

rocks (precariously balanced rocks likely to be toppled by strong-enough seismic activity) 

as strong-motion seismoscopes at the Earth’s surface to constrain the probability of seismic 

ground motions (Brune and Whitney 2000). Seismic and igneous understanding gained 

while characterizing Yucca Mountain will benefit future repository programs located in 

active seismic areas or in areas that have had geologically recent igneous activity. 

The Yucca Mountain program significantly advanced the state of scientific knowledge in 

several areas related to seismic and igneous hazards. In these areas, rigorous state-of-the-art 

Contributions from the Yucca Mountain Program 35 
expert elicitations and probabilistic seismic and volcanic hazard analyses led to significantly 

more robust fundamental understanding of the phenomena and substantially improved 

technical bases for risk calculations.24 (According to the license application, some of the 

greatest risks result from low-probability, high-consequence events in the igneous and 

seismic scenarios.) Future repository risk also may be driven by extremely low likelihood and 

potentially high-consequence events, which suggests that they be considered a primary technical 

factor for repository siting determinations. 

Performance Confirmation 

In submitting its license application to the Nuclear Regulatory Commission in June 2008, 

DOE was attesting to its belief that its natural-system characterization and modeling met 

compliance requirements. Research on the natural system did not stop at that point, however, 

for two reasons. First, Nuclear Regulatory Commission regulations require a continuing 

research program (known as a “performance confirmation program”) as a condition for 

granting the license to construct the repository. The purpose of the program, as its name 

implies, would be to evaluate the adequacy of assumptions, data, and analyses underlying 

the construction license. The program and subsequent programs specified under a license to 

operate would continue until repository closure, which could be well over a 100 years after 

emplacement of the first unit of waste in the repository. The second reason for continued 

research on the natural system is to increase understanding of its behavior. Increased 

understanding can lead to reduced uncertainty and greater confidence in the technical 

community about repository behavior. Increased public confidence was a major reason for the 

Science and Technology program that OCRWM initiated in 2002 (Chu 2002). 

Designing and Excavating Site-Characterization Facilities 

The 1993 DOE site-characterization annual plan included plans for extensive tunneling into 

the planned geologic repository block to gain visual and testing access to the site’s geology 

(NWTRB 1993: 2). Before the beginning of underground tunneling in 1994, surface-based 

testing consisted of trenching, outcrop examination, and vertical boreholes that provided 

almost 200 small-diameter (1- and 2-inch) cylindrical specimens to test geophysical access, 

but most of the boreholes were located outside the repository-block boundary and had 

orientation and other limitations. The importance of direct tunneling into the mountain 

was emphasized by the Board (NWTRB 1992: 16-17) because the tunneling provided 

24For example, in 2008 DOE’s lead laboratory issued a probabilistic volcanic-hazard assessment update 

that resulted from a rigorous four-year study (SNL 2008e). The study methodology (closely following U.S. 

Nuclear Regulatory Commission guidance on using expert elicitation in probabilistic hazard assessment 

[Kotra et al. 1996; Budnitz et al. 1997]) was based on a formalized expert elicitation and included a series of 

independent expert briefings in which all available data and interpretations were presented and considered, 

multiple field excursions were conducted, and aggregated and weighted conceptual and numerical models 

were produced and analyzed. The study drew on state-of-the-art data and analytical techniques in both 

geosciences and statistics. The 2008 study, which included consideration of repository disruption by dikes, 

sills, and erupting columns and vents, estimated the probability of repository disruption as 3.1x10-8 per year, 

slightly higher than previous estimates. 

36 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
opportunities for exploring continuous sections of the repository block to identify geologic 

features, obtaining representative-size specimens for laboratory testing, and conducting in 

situ performance field-testing. 

The Yucca Mountain program’s exploratory tunnel was delayed and incurred high costs 

because of DOE decisions to contract for larger-than-normal custom excavating equipment 

and not to consult and incorporate the experience of practicing specialists at early stages 

(NWTRB 1993: 22-24). Part of the reason for the decisions may have been a perceived 

pressure to build the repository. DOE opted for large tunnel diameters in 1990 (NWTRB 

1992:16) and contracted for the construction of a 7.6 m- (25 ft.) diameter, special-design 

tunnel boring machine (TBM) to excavate the tunnel, named the exploratory studies facility 

(ESF). The Board was concerned that the tunnel diameter was overly large and that it would 

lead to higher costs and delays. The Board had suggested that the “tunnel size” (diameter) be 

no greater than functionally required for early access and exploration of the geologic block” 

(NWTRB 1992: 17). The most frequent argument made by DOE and the M&O contractor 

in support of large tunnels was that the large diameter was needed for possible ventilation 

purposes as part of the future repository design (NWTRB 1998: 15). 

DOE excavated the large-diameter 7.9 km (4.89 mile) ESF tunnel over about 31 months, 

yielding a net production rate of about 12.3 m (40.4 ft.) per working day (NWTRB 

1998: 15), which is slow compared with conventional tunneling (NWTRB 1993: 16) and 

considerably lower than the planned excavation rate of 30 m (100 ft.) per working day. 

The tunnel diameter was much larger than was needed for site characterization and led to 

several problems and inefficiencies. Excavating smaller tunnels is preferable for future site 

investigations for several reasons (NWTRB 1993: 16). Smaller-diameter tunnels are more 

stable structurally, particularly when excavating in fault zones and rock of low quality. They 

could allow eliminating some or all ground support. They also would be less expensive 

to maintain. A smaller TBM is more efficient and more cost-effective because a smallerdiameter TBM advances faster through rock. Construction risks, delays, and expense also 

increase with increased tunnel size. More time is required to install additional rock support 

where needed and more frequent TBM maintenance is needed because of larger, less 

reliable components and more frequent cutter changes. In addition, because DOE planned 

to incorporate the ESF into the repository, costly and time-consuming quality-assurance 

procedures that would be unnecessary for a site-characterization construction project 

were required. A possibly overriding, although nontechnical, reason for not using tunnel 

diameters larger than necessary for site characterization might be to avoid any appearance of 

prebuilding the repository. 

Future repository developers should carefully consider (1) the size of tunnels needed for site 

characterization; (2) the use of off-the-shelf excavating equipment when possible; and (3) 

obtaining assistance from geoengineering experts early in the decision-making process. 

Contributions from the Yucca Mountain Program 37 
3.4. ENGiNEEriNG AND PrOTOTYPiNG 

Engineering Program 

DOE initially viewed the Yucca Mountain program primarily as a science program with a 

straightforward objective: gather and analyze sufficient information to determine whether 

Yucca Mountain is a suitable site for a deep geologic repository. Although there were 

many positive early indicators that geologic disposal in a thick unsaturated zone in the 

arid Southwest would be satisfactory (e.g., Winograd 1974; Roseboom 1983), there was 

insufficient information to be certain. Information was gathered and analyzed, and, at some 

point, DOE determined that the site was suitable.25 

At that point, what had been a science program became an engineering program. That did 

not mean that the need for science vanished or even decreased. In fact, science continued to 

have an important role in providing information for design and for the TSPA-LA, a critical 

element of the license application. Rather, it meant that the objective of the Yucca Mountain 

program had changed. No longer was the objective to determine site suitability and thus 

whether the Secretary of Energy should take the formal step required by Section 114 of 

the NWPA of submitting a recommendation to the President that the President approve 

Yucca Mountain as a site for repository development. Now the objective was to do what was 

necessary to design, license, build, and operate a repository at Yucca Mountain within the 

framework of the U.S. waste-management system. 

In the context of a long-term repository, the term “engineering program” means a 

large, complex project that involves siting, design, permitting, licensing, construction, 

and operation; that lasts many years; and that requires a substantial amount of science 

and technology, some of which may be new. An engineering program first needs to be 

recognized as such, and then it needs to have a management and organizational structure 

that can integrate all aspects of the project, including public information, scientific 

studies, site characterization, engineering development and testing, design, procurement, 

construction, operation, and closure with an overall view of the whole system. Continuity 

of managerial and technical leadership, consistent funding, and the right incentive 

structure for completing the work are essential pieces and parts of the successful structure. 

Many scientific investigations may be needed to support the program, but management 

cannot lose sight of the fact that the science is there to support the needs of the 

engineering program. 

The design of a deep geologic repository at Yucca Mountain was, by its very nature, 

an engineering problem of the first order. It had a clear objective, involved numerous 

constraints, presented unprecedented challenges, and required many choices to be made— 

25Pinpointing exactly when DOE made that determination is difficult, but it came well before the formal 

determination by the President and Congress in 2002. 

38 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
all hallmarks of a classic engineering design problem. However, this was a design problem 

the likes of which humanity had never before attempted, because it involved a time scale that 

required predictions of material and system behavior tens and hundreds of thousands of 

years into the future. Some perspective on the uniqueness of this temporal projection comes 

from the realization that the most ancient monuments of past engineering achievement, 

such as Stonehenge and the Pyramids, are barely five thousand years old. 

The approach to any engineering problem takes advantage of experience and scientific 

knowledge. In the case of a repository in Yucca Mountain, at the outset there was little direct 

repository-engineering experience, and the available scientific knowledge had significant 

gaps. Natural analogs can provide some insight and guidance for making design decisions, 

but such “found experiments” are rare and their lessons are limited by the very fact that they 

are analogs rather than models. There was, of course, experience in relevant technologies, 

such as mining operations, and knowledge of basic scientific principles, such as subsurface 

hydrology, but this experience and knowledge had to be adapted to the new conditions, 

constraints, and challenges of the unprecedented problem of a repository. 

Engineers are used to working with a paucity of experience, and they have demonstrated 

time and again that new challenges can be met. The Manhattan Project and the Apollo 

Program are two outstanding examples of first-of-a-kind challenges to engineers. The two 

programs were unique in the need for collaboration between engineers and scientists. The 

Manhattan Project launched nuclear energy, and the Apollo Program was the outstanding 

early accomplishment of human space flight. The naval nuclear propulsion program 

provides a similar story of a successful engineering program. It seemed to the Board that 

DOE was not exhibiting the same commitment to the engineering-development process in 

the Yucca Mountain program. 

Gaps in scientific knowledge often can be filled by the results of research programs, and this 

was what the Yucca Mountain program seemed to focus upon. Even after site suitability had 

been established, many open questions remained about such phenomena as the movement 

of water in the unsaturated zone and the corrosion of metals in an oxidizing environment, 

and the questions presented relatively well-defined engineering-scientific problems about 

which researchers could hypothesize, devise experiments, collect data, and present results. 

Because the areas of research were unexplored, the work produced new knowledge. The new 

knowledge clearly benefited the models used in the probabilistic risk assessments that were a 

principal part of the license application. 

Science and the preparation of a license application, including probabilistic risk assessments, 

tended to overshadow the design aspects of the Yucca Mountain program, which continued 

to be a neglected area. When public presentations were made on the design of surface 

facilities, for example, their content often lacked detail. It became increasingly obvious 

Contributions from the Yucca Mountain Program 39 
that the engineering aspects of the program were subordinate to the scientific and license 

considerations. When questions were raised about prototyping and demonstration 

programs, they were dismissed as less important because the equipment involved was 

commonly used in mines and other analogous operations. This may well have been the 

case for the invert, but the application of the equipment for emplacing drip-shield sections, 

for example, was as unique as the drip shield itself and should have been the subject of 

a well-considered prototyping program culminating in a full-scale demonstration that 

the tasks could indeed be carried out successfully. In a recent presentation to the Board, 

a seasoned mining engineer pointed out the uniqueness of the drip shield and the dripshield emplacement device, as well as the difficult conditions for drip-shield emplacement 

(Kendorski 2005). 

Although DOE began transitioning from a science program to an engineering program 

in the late 1990s, engineering did not seem to arrive at its proper place in the Yucca 

Mountain program until about mid-2006, when DOE management acknowledged that 

engineering should be driving the program. That led to the completion and submittal of 

the long-overdue license application to the Nuclear Regulatory Commission. However, 

with the subsequent decision by the Administration to terminate the Yucca Mountain 

program, deep geologic disposal activities have been relegated to a small, generic 

science program in DOE’s Office of Nuclear Energy, pending recommendations from 

the Blue Ribbon Commission on America’s Nuclear Future and subsequent action by 

Administration and congressional policy-makers. 

Among the principal lessons learned from the Yucca Mountain program should be that an 

engineering program should from the outset be recognized as such and be managed and 

operated accordingly. This means that it should be viewed not so much as a research and 

development program but rather as a development and research program, with the engineering 

goal of developing the final design for a repository being foremost. 

The ultimate design and operation of the system always should motivate the objectives 

of the appropriate scientific research and expect them to be in service to the engineering 

objectives. The aerospace engineer Simon Ostrach has described such prioritizing as 

Research for Development (R4D), with the design objective in the driver’s seat (Ostrach 

2008). Admiral Rickover’s nuclear naval propulsion program was an excellent example of 

the success of this philosophy. 

Another lesson is that of the need for continuity of management, personnel, and funding. 

Contractors came and went, and managers cycled in and out, while the amount of money 

available in the next fiscal year was always in doubt and not under the control of the 

40 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
management of the program. Any engineering program would benefit greatly from having 

a dedicated organization that would maintain continuity of its personnel, especially of its 

management and principal engineers and scientists. 

Prototyping 

The French, whose success in the development and use of nuclear power is well known, have 

done significant prototype testing of the engineered systems they plan to use in relation to 

waste disposal. When the Board visited nuclear development sites in France in 2008, the 

French commitment to prototype testing was clear. Not only would such testing serve to give 

the public confidence in the approach being used but it also would provide a firm basis for 

the French license application. 

Similarly, Svensk Kärnbränslehantering AB (SKB), the utility-owned company responsible 

for the Swedish waste-management and repository programs, has had prototype programs 

under way for many years for the waste package, for the equipment used to weld the lid 

onto a loaded waste package, and for the equipment used to emplace the waste packages 

in the repository, as well as other novel equipment items. As in the French program, these 

prototype efforts build public confidence, help explain the program, and provide valuable 

information for a license application. Tangible, working items at or near scale that can 

be observed and discussed help build public confidence (Coleman 2010). Several Board 

members visited the Swedish and Finnish repository programs in 2006. Sweden and Finland 

cooperate closely in repository development because they plan to dispose of high-activity 

waste in similar geologic media using the same repository design. 

Prototyping and testing of engineered systems are necessary to enhance confidence in their 

feasibility and to adjust designs. Any engineered barrier system is likely to have unique 

design features that are important for performance and that therefore need to be confirmed. 

For example, in the Yucca Mountain design, the drip shield, the waste package, and the 

pallet were in this category. In addition, equipment designed to emplace the drip shield and 

waste package and the equipment used to make and examine the final closure welds of the 

waste package also need confirmation. 

To its credit, DOE began work on planning its prototype program in the mid-1990s, which 

put the program on a fast track when site suitability was determined. However, the only 

aspects of a prototype program that were implemented were the waste package and the 

equipment for welding the double lids onto a loaded waste package, and these aspects 

were only partially implemented. For example, at one time, nine full-scale waste package 

prototypes were part of the planned waste package prototype program. Yet, the waste 

package prototype program built only one full-scale waste package and several full-scale 

Contributions from the Yucca Mountain Program 41 
waste package sections. The information gained was invaluable and affected the final waste 

package design. Early prototyping also demonstrated the impracticality of shrinkfitting the 

two cylinders of the waste package together, so an early design that called for shrinkfitting 

was rejected. Prototyping also exposed some issues in heat-treating the waste packages and 

in the design of the weld grooves. The system for welding and inspecting the final closure 

lids onto the waste package was developed at full scale by Idaho National Laboratory 

personnel and demonstrated at full scale in Idaho Falls, Idaho. It was a success, although 

only one full lid weld was performed. 

At least the waste package prototype program and the final closure weld system produced 

some results. DOE had prototype programs on the books for the drip shield, the pallet, the 

invert, and the drip-shield emplacement equipment, but these programs never began. This 

is a particularly significant omission for the drip shield and the drip-shield emplacement 

equipment because TSPA calculations indicate that drip shields are important for repository 

performance, at least with respect to the models implemented and their assumptions. 

If the prototype programs for the drip shield and its emplacement equipment had been 

implemented, the information obtained may have been useful in the licensing process. 

Another obvious candidate for prototyping was the TAD canister. DOE issued two contracts 

for designing and building a TAD canister. The contracts both produced designs, but the 

contracts were terminated without fabricating prototype TAD canisters. 

Future repository programs should include the development of prototypes of novel equipment 

items, such as the waste package, the platform that the waste package rests on, any novel 

instrumentation, and any novel equipment used to emplace, move, or install other 

equipment items. 

Drift Degradation During the Preclosure Period 

Drifts normally degrade over time because of rockfall, flaking, dust, seepage, seismic events, 

and other natural phenomena. This degradation process likely would deposit debris on the 

invert, the rails, and the emplaced waste packages. The debris could obstruct the movement 

of waste packages into the drifts, a process DOE intended to accomplish remotely using 

emplacement vehicles. Clearing obstructions would be challenging because it also would 

be done remotely because of the high-radiation environment. DOE assumed that there 

would be no drift degradation at Yucca Mountain during the 50- to 300-year preclosure 

period. DOE also had confidence that the emplacement-drift ground support system would 

function effectively. The technical basis for DOE’s confidence was not apparent. Further, 

DOE had not developed contingency plans for cleaning and removing debris from the 

invert and the rails before emplacement of the drip shields. Future programs should take 

potential preclosure drift degradation into account, particularly if the preclosure period is long. 

42 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
Future repository programs should systematically evaluate the likelihood and consequences of 

drift degradation during the preclosure period and, if necessary, design appropriate measures 

for preventing such degradation or mitigating its effect. Future programs also should consider 

developing plans for cleaning and removing debris. 

3.5. iNTEGrATED TOTAL WASTE-MANAGEMENT SYSTEM 

Transportation-Aging-Disposal Canister 

The NWPA requires DOE to provide transportation casks and other equipment needed 

for transporting SNF from commercial nuclear power plant sites to a repository site. 

Beginning in the mid-1980s, DOE undertook the Cask System Development Program 

(CSDP) and contracted with cask manufacturers to design transportation casks of four 

sizes for transporting SNF from utility sites. The casks in the CSDP were being developed to 

transport bare fuel without any internal canister. Before work on the CSDP was completed, 

however, it was largely superseded by the Multipurpose Canister (MPC) program. In the 

MPC program, multiple SNF assemblies would be contained in sealed thin-wall metal 

canisters that would be placed in a range of casks for storage and transportation. The MPC 

program was terminated by congressional action in 1996. 

DOE’s most recent canister-design program was identical in concept to the MPC program. 

In the new program, multiple commercial SNF assemblies would be placed in TAD canisters 

at utility sites, and the canisters would be placed in a storage cask, a transportation cask, 

or a disposal cask (waste package), depending on the next function for the loaded canister. 

Movement of the SNF from one function to the next would simply be by moving the 

loaded canister from one cask to another. Work on the TAD canister program began in 

2005 (DOE 2007) but was halted in 2009, following initial actions by DOE to terminate the 

Yucca Mountain program. The TAD canister program and the previous MPC program were 

significant steps forward in recognizing the benefit of preventing repetitive handing of bare 

fuel. The programs also introduced the concept of standardizing container designs, with the 

attendant economies in package fabrication, loading, and subsequent handling operations. 

Unfortunately, because these concepts were not successfully introduced in the program 

earlier, there already is a large and growing quantity of SNF in storage at utility sites in a 

wide and widening range of container types. 

Two additional aspects of not introducing the TAD canister earlier in the program could 

have proved problematic. By the time the TAD canister concept was introduced, wastepackage designs had been fixed and much of the conceptual design of the surface facilities 

at the Yucca Mountain site had been completed, which limited the maximum size of a TAD 

canister. Many reactor sites could accommodate a larger canister, however, and, in fact, are 

using MPC-like dual-purpose (storage and transportation) canisters that are larger than 

the largest TAD canister permitted by the Yucca Mountain program. In addition, DOE 

Contributions from the Yucca Mountain Program 43 
specified the capacity of the TAD canisters and the maximum length of the spent fuel that 

TAD canisters would be expected to accommodate. This resulted in a TAD canister design 

that cannot accept some SNF, such as the SNF assemblies from South Texas Project reactors, 

which are longer than the fuel used in other U.S. PWRs (~14 ft vs. ~12 ft). Future reactors 

also could use this longer fuel. Future programs should consider the TAD canister concept 

carefully because of its potential safety, handling, system-simplification, and cost advantages. 

However, the programs should ensure that the sizes of the canisters are compatible with fuel 

dimensions and the sizes of dual-purpose canisters. 

Nuclear utilities are moving increasingly to dry-storage systems. For most dry-storage 

systems, the SNF is sealed into large metal dual-purpose canisters, and the canisters are 

placed in massive shielded casks or structures. As mentioned, many dual-purpose canisters 

already are too large for the repository design in the license application submitted to the 

Nuclear Regulatory Commission by DOE, and the trend is toward larger canisters. Other 

canister issues also exist. For example, the nuclear criticality regulations for canisters 

(either 10 CFR 63, which applies to Yucca Mountain, or 10 CFR 60, which applies to other 

repositories) have not been tested through an entire licensing process. Thus, not known is 

whether the dual-purpose canisters that already are loaded or will be loaded in the future 

would meet the criticality requirements of the disposal regulations, especially for longaged and high-burnup SNF. Certainly, however, the Nuclear Regulatory Commission 

would have to allow burnup credit for both actinide depletion and fission products for 

there to be any chance that dual-purpose canisters loaded with SNF could meet repository 

regulatory requirements. DOE worked on the burnup credit issue for at least 15 years in 

the Yucca Mountain program, although the degree of management priority accorded to 

the issue varied widely. Because the burnup credit issue applies to any repository, DOE 

should continue to vigorously pursue the burnup credit issue because it is important to storage, 

transportation, and disposal of SNF. 

The experience with TAD canisters and the fact that current dual-purpose canisters are too 

large for the Yucca Mountain design in the license application argue strongly for addressing 

the entire waste-management system from at-reactor to final disposal as a whole at the earliest 

possible stage of any new program. 

Future waste-management programs could benefit from any action that can be taken now, or 

in the near term, to specify requirements for SNF package designs to utilities and cask vendors. 

This would be in the overall interests of the program because it would prevent continuing the 

loading of a wide range of container and cask types, which may result in a requirement for 

repackaging before transportation of the containers and casks from the reactor sites or following 

transportation to a repository. This is especially important for the utilities whose reactors will 

reach their final shutdown date before the implementation of a disposal program for SNF 

from commercial nuclear power plant sites. 

44 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
Transportation 

As noted earlier, the TAD canister concept had the advantage of minimizing the handling of 

SNF. However, there are transportation issues involving TAD canisters. 

Loading of TAD canisters at a commercial reactor site would require a handling system with 

a minimum 100-ton lifting capacity. The current equipment configurations at many sites 

would not meet this threshold (TriVis 2005). Each of those sites would require an upgrade 

to its cranes’ lifting capacity, incurring significant expense and possibly creating operational 

downtime. At some facilities, the extent of the required upgrading could be cost-prohibitive, 

requiring other operations to be arranged, possibly including transportation of SNF from 

the facility for loading into TAD canisters at another location. 

At many sites, short-line (locally and regionally owned) railroads likely would have been 

relied on for transporting TAD canisters and their overpacks to transfer points, where the 

short-line railroads would connect with the mainline railroad network (DOE 2008a). Many 

of these short-line railroads would require significant upgrades to meet DOE’s minimum 

track-quality standards. If these short-line railroads could not be upgraded—perhaps 

because of the expense involved—other, more logistically complicated, modes would have 

had to be used. 

Perhaps the major transportation issue, however, was the lack of connection of the Yucca 

Mountain site to the national railroad infrastructure. Making the connection would 

have required construction of a new 330-mile line from the Caliente, Nevada, mainline 

railhead to Yucca Mountain at an estimated cost of approximately $3 billion (DOE 2008b). 

Significant delays in constructing the new line would have reduced the efficiency of the 

repository construction project, delayed the start of repository operations, and potentially 

changed the characteristics of the waste stream arriving at the repository. If the new line 

were never constructed, the feasibility of the entire Yucca Mountain program would have 

been at risk. No contingency plan appeared to have been developed to address the possibility 

that the new line might not be built (NWTRB 2004; NWTRB 2006). 

In its surface-facility design and in its throughput analysis of the Yucca Mountain 

receipt facility, DOE assumed that 90 percent of the commercial SNF would arrive at the 

repository site packaged in TAD canisters, although this assumption was acknowledged 

to be questionable. The 10 percent of the commercial SNF not packaged in TADs would 

be received at the waste-handling facility (WHF) on the repository site, where the fuel 

assemblies would be transferred to TAD canisters. However, the WHF was designed with 

limited capacity, and if more than 10 percent of the commercial SNF did not arrive in TAD 

canisters, backlogs would have been created, forcing additional amounts of commercial 

SNF to be placed on storage pads. Alternatively, there would have been a need to construct 

additional WHFs. 

Contributions from the Yucca Mountain Program 45 
This requirement for repackaging uncanistered SNF into TAD canisters at the repository site 

may not, at first sight, appear to be an issue that has a particular bearing on the requirements 

of the transportation system. Any difference between the quantities of SNF assumed to 

be loaded in TAD canisters at the nuclear power plant sites and what might happen in 

practice would change the numbers and types of casks needed for fuel storage, as well as 

the requirement for cask-handling equipment, maintenance, and other issues, such as the 

logistics of the transportation program. This underscores the requirement for recognizing 

the interdependencies of the design of the fuel cycle and the program for transporting highactivity waste. 

The research and development plan developed by DOE’s Office of Nuclear Energy appears 

to take the Yucca Mountain experience into account and to recognize the significance of the 

transportation function as an important and integrated component of any system design 

that emerges (Schwab 2010). 

Integration of the Total Waste Management System 

Despite the fact that the Yucca Mountain program is a total system consisting of waste 

acceptance, transportation, handling and repackaging, emplacement, and eventual closure 

and monitoring, there was little evidence of efforts to manage it as a total system until the 

early 2000s. By then, a complicating factor had entered the equation: Utilities began to sue 

DOE for nonperformance under the Standard Contract (10 CFR 961), and DOE would 

not talk with utilities outside the courtroom, complicating understanding of characteristics 

of the front end of the total system. Also complicating management of the program as 

a total system was the organizational scheme chosen. Scientists and engineers stationed 

in Las Vegas, at National Laboratories, or at the USGS offices in Denver were focused on 

the repository. The responsibility for waste acceptance and national transportation was 

located in Washington, D.C., and the majority of the people supporting those activities were 

located there. Headquarters for OCRWM also was located in Washington, but the majority 

of OCRWM employees were in Las Vegas. During the 1990s and before, scientists were 

splintered into many independent groups by discipline and by their locations—many of 

which were hundreds of miles from program offices in Las Vegas. Communication among 

scientists, engineers working on the repository design, and analysts working on performance 

assessments did not result in effective coordination. Despite the fact that waste management 

and disposal is a total system, it was not being recognized and treated as one. 

Regardless of the institutional form selected for future repository programs, they are likely 

to face the same issues of communication and coordination among scientists, engineers, 

and performance-assessment analysts. Handling and transportation of the waste need to 

be resolved in a timely manner to ensure that schedules are met for testing, startup, and 

successful operations. For the Yucca Mountain program, there was little evidence that such 

46 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
activities were effectively integrated into the overall program plan, particularly in relation to 

the program schedule. 

Ultimately, the success of the Yucca Mountain repository as a total system would 

have depended on the smooth integration of its transportation, surface facility, and 

emplacement operations. There were computer simulations of the integrated system, 

but, except in a notional sense, they did not and could not incorporate the real-world 

complications of system and machinery bottlenecks and breakdowns, not to mention 

downright inoperability for reasons revealed only in a full-scale or near-full-scale pilot 

plant. As a result, the design and functionality of the repository surface facilities were 

not well integrated with the balance of the waste-management system. Information was 

lacking on a comprehensive integrated throughput model for the surface facilities with 

time steps compatible with the task durations. The assumptions that input for each facility 

would be available when needed and that output would be removed when processing 

is complete do not represent a realistic situation, nor was any justification for the 

assumption of an availability26 of 75 percent provided. Too few operational details were 

presented to the Board to obtain an understanding of the various operations and how they 

interacted, especially during upset conditions. Future programs must take integration of 

the entire system into account. 

Managing High-Burnup Spent Fuel 

Before 2000, most fuel discharged from nuclear power plants in the United States had 

burnups below 45 GWd/MTU, which is considered the threshold for high burnup. SNF 

burnups of 45-50 GWd/MTU are typical currently, and burnups of over 60 GWd/MTU are 

expected to be routine in the future. Consequently, although there is considerable experience 

with storage of low- to moderate-burnup SNF, both in reactor pools and at dry-storage 

facilities, there is little experience with storing high-burnup SNF, the likely dominant SNF 

form requiring future storage. 

In parallel with the trend to higher burnups, the likely storage period for SNF before 

processing or disposal has been increasing, with storage periods of 100 years or more 

now foreseen. The termination of Yucca Mountain is one of the principal reasons for this 

increase. Although the performance in the reactor of fuels designed for higher burnups is 

established, the effect on fuel integrity of storage over such long periods and the subsequent 

behavior of that fuel in handling or transportation is not known, particularly for highburnup SNF. 

26Availability is the time that a structure, system, or component is capable of performing its intended function as a fraction of the total time that the intended function may be demanded (NEI 2007). 

Contributions from the Yucca Mountain Program 47 
Under the current U.S. regulatory framework, a safety basis has been demonstrated by 

licensees for dry storage of SNF for 60 years. A safety basis has not been developed, however, 

beyond this period of time. Of particular concern are the potential effect of long-term aging 

on SNF and the degradation of storage-system structures and components, both of which 

have implications for cladding integrity, criticality safety, and offsite radiation dose in both 

normal and off-normal conditions. Complicating matters is the fact that the dry-storage 

systems have varying contents, designs, and applications, as well as being located at different 

facilities with different environments. Consequently, there is not yet adequate experience 

to give the necessary assurance that SNF and the storage canisters in which it is loaded will 

be in a suitable condition for future transport operations after extended storage periods. 

Moreover, the extent to which the fuel may need to be repackaged before transport also is 

not known. 

DOE, the Nuclear Regulatory Commission, and the nuclear industry have recognized 

the need to approach high-burnup considerations as an integrated system involving 

interdependencies among storage, transportation, disposal operations and, potentially, 

reprocessing. The goal of this effort is to take these considerations into account as new fuel 

designs and transport packages are developed. 

There is another issue that has not yet become a focus of the nuclear industry, although there 

is an increasing realization that it must be addressed. Although the performance of advanced 

fuel designs in the reactor is well-established, the need to extend the periods during which 

SNF will require storage means that it is important also to take this into account in the 

design of new fuel types. A small penalty in fuel performance in the reactor resulting in a 

major advantage during the storage, transport, and disposal of SNF could have significant 

overall economic benefit for the nuclear power plant operator; these sorts of trade-offs 

warrant detailed assessment. These developments, both individually and collectively, 

offer opportunities for fully recognizing interdependencies in the transportation wastemanagement system as part of the system design process. 

3.6. PErfOrMANCE ASSESSMENT AND iNTEGrATiON 

Performance Assessment 

Given the enormous problem complexity and inherent uncertainties, probabilistic modeling 

and simulation is the only viable way to predict quantitatively the long-term performance 

of a geologic repository such as Yucca Mountain. The well-established discipline of 

probabilistic risk assessment (PRA) provides the necessary methodological framework, 

modeling principles, and tools for this purpose. PRA is of particular value when the 

likelihood of possible future states of the physical system and governing phenomena are 

poorly known and are best described by discrete or continuous alternative scenarios. In that 

case, PRA provides a probabilistic framework that couples the scenarios with deterministic 

48 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
representations of the underlying system and processes. The probabilistic model used by 

the Yucca Mountain program is known as Total System Performance Assessment, or TSPA. 

DOE developed numerous iterations of TSPA in the course of its investigations of Yucca 

Mountain. The first iterations were rudimentary, although the most recent iteration, known 

as TSPA-LA (license application), was the most sophisticated. TSPA-LA represented the 

culmination of the most thorough study of the performance of a geologic repository for 

high-activity waste ever performed by U.S. scientists and engineers.27 

Although TSPA-LA deviated from some of the more-accepted PRA practices in modeling 

risk scenarios and in final representation of risk metrics, as discussed later in “Measuring 

and Portraying Risk,” it relied heavily on PRA technology and also offered several 

methodological innovations and advancements.28 

The major components of TSPA-LA included models of the waste; the engineered barrier 

system, including waste package and drip shield; the natural barrier system, including the 

hydrogeologic unsaturated and saturated zones; and the biosphere. Scenarios considered 

included the nominal scenario, earlier-than-predicted failure of engineered barriers, and 

seismic and igneous events. The events that were included had an estimated frequency of 

occurrence equal to or greater than 0.0001 per year for 10,000 years (or 1 in 100 million). 

The period of analysis, generally on the order of 20,000 years in TSPAs produced before 

2004, was extended to 1,000,000 years in TSPA-LA. 

TSPA provided a quantitative estimate of expected (probability weighted) radiological dose 

to humans associated with a geologic repository at Yucca Mountain. This quantitative 

measure was based on estimates of the likelihood of events and processes leading to 

exposure, and on the consequences of those events (in terms of dose to the human 

population). Uncertainties associated with models and input parameters were estimated 

and propagated through the entire TSPA model to obtain an uncertainty distribution of 

the expected dose. Advanced statistical techniques were used to identify the relative effect 

and significance of individual repository characteristics in the TSPA calculations. Results 

of those analyses were valuable for identifying fruitful areas for further investigation and 

risk reduction. 

27TSPA-LA undoubtedly was informed by and benefited from experience gained from previous performance 

assessments of other complex projects, particularly the performance assessment developed to obtain compliance certification for WIPP (DOE 1996). In fact, many of the scientists and engineers who participated 

in developing TSPA-LA also had been involved in developing the WIPP performance assessment. 

28A major issue with TSPA-LA as a performance assessment is its strong orientation toward a regulatorycompliance case. This manifests itself in sometimes excessive and unrealistic use of conservative bounding 

analyses that limit understanding of the true performance of the system. Risk analysis, on the other hand, 

aims at providing the most realistic assessment of performance on the basis of the current state of knowledge, accounting for knowledge gaps and other sources of uncertainly with probability distributions. If 

done correctly and consistently, the compliance case could be a natural byproduct of the risk analysis. 

Contributions from the Yucca Mountain Program 49 
TSPA was used to estimate the contribution to repository waste-isolation performance 

from each of the barriers (engineered and natural) over time. TSPA provided the capability 

to identify the particular radionuclides that contributed the most to risk.29 Because of 

radioactive decay, the dominant risk-contributing radionuclides vary by time and by 

scenario. TSPA demonstrated that probabilistic dynamic modeling of large, complex 

natural and engineered systems can be performed. Output from a “Simplified TSPA” (SNL 

2008f) developed late in the Yucca Mountain program was broadly consistent with the full 

TSPA and helped to improve confidence in the conceptual basis of the TSPA. Conceptual 

and numerical models of unsaturated fluid flow and radionuclide transport in fractured 

unsaturated rocks advanced as a result of Yucca Mountain studies. Many improvements were 

made as the models evolved with respect to computational tools, conceptualization of the 

host-rock physical properties, and improvements in conceptualization and representation of 

the transport of heat and mass in the waste-package environment. These models, sometimes 

abstracted to save computer time, were incorporated into TSPA. 

Advancements in the state of the art in relation to the development of TSPA-LA provide 

many analytical and computational foundations that can be used in future studies of 

geologic repositories. In the area of characterizing and assessing uncertainty, TSPALA pushed the state of the art to higher levels, including (in selected cases) explicit 

treatment of uncertainties associated with models and abstractions, assessment and 

propagation of parametric uncertainties,30 and separation of uncertainty resulting from 

the natural variability of physical phenomena (aleatory uncertainty) and knowledge-based 

uncertainty (epistemic uncertainty). Separation of sources of uncertainty provides the 

opportunity to identify knowledge gaps that are potentially significant in a risk-informed 

decision-making framework. 

The bounding analyses of the TSPA-LA were important to managing the scope of the 

assessment and demonstrating compliance with dose standards. The Yucca Mountain program 

conducted multiple sensitivity studies using the full TSPA-LA and used a simplified TSPA 

to explore the effect of variations on some key assumptions and parameters. The objective of 

one such study, performance margin analysis, discussed later, was to develop a more realistic 

assessment of key processes and variables and related site performance than embodied in the 

“compliance model” TSPA-LA with its inherent conservatisms in the face of knowledge gaps 

and data limitations. Some limitations of this study are discussed later in this section. 

29Besides its utility for a Yucca Mountain repository, such information would be extremely valuable in 

possibly influencing the future consideration of chemical separation of radionuclides to benefit repository 

designs. 

30The TSPA lacked total consistency in this area, however. In some cases, single values rather than uncertainty 

distributions were used; in other cases, probability-based distributions were used but without supporting data. 

50 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
The strength of an integrated model such as TSPA-LA is that the merits of the methods used 

and results obtained can be evaluated and debated by the informed scientific and technical 

community, as well as by regulators. In fact, an international group of experts assembled 

to review the version of TSPA performed before TSPA-LA concluded that this assessment 

represented a competent modeling effort in keeping with international practice (IRT 2002). 

Two general and 27 specific recommendations were made to improve the assessment. 

DOE addressed all of the recommendations and documented their disposition in an 

appendix to TSPA-LA (SNL 2008c). A later expert review also was conducted (BSC 2006). 

The performance assessment, although not perfect, was nevertheless a first-of-a-kind and 

provided a benchmark for future studies. It had the capacity for continuing to evolve and 

improve by capturing and embodying the latest advances in scientific understanding and 

engineering practice. 

Enactment of the Energy Policy Act of 1992, P.L. 102-486, started the process by which 

regulations and standards for high-activity waste repositories became bifurcated in the 

United States. The United States now finds itself in the situation of having two sets of 

repository regulations and standards. One set, 10 CFR 63, 10 CFR 963, and 40 CFR 

197, applies only to Yucca Mountain; the other set, 10 CFR 60, 10 CFR 960, and 40 CFR 

191, applies to all other U.S. repositories. The set applying to other repositories has been 

essentially stagnant since the early 1990s. The set applying to Yucca Mountain has been 

shaped by extensive study, rule-making processes, hearings, and judicial decisions that have 

taken place since passage of the Energy Policy Act of 1992, and to some extent are still taking 

place today. As a result, the two sets of regulations and standards have many significant 

technical differences. 

From a performance assessment point of view, an important difference is that the Yucca 

Mountain regulation (10 CFR 63) allows and requires that the performance of the total 

repository system taken as a whole be used to determine whether the site is acceptable and 

whether the repository meets the dose criteria specified in the regulation. Although the 

regulation (10 CFR 60) applying to other U.S. repositories allows performance assessment to 

be used, it also contains distinct criteria for various subsystems of a repository. 

Any new repository program will require a regulatory framework for its site selection, 

characterization, and subsequent activities. That framework exists but it is dated and has 

not benefited by advancements made in almost two decades. Repository developers must 

anticipate that the framework may change. The Board believes that the use of total system 

performance assessment should be required in the regulatory framework. 

Contributions from the Yucca Mountain Program 51 
Measuring and Portraying Risk 

In part because PRA is now a well-established and demonstrated methodology (Garrick 

2008), there is a definite trend toward using risk-based approaches to making decisions 

about high-hazard activities. To ease the transition from traditional (i.e., deterministic and 

prescriptive) methods of safety analysis and attendant rules and regulations and its legacy 

comfort zone, the Nuclear Regulatory Commission has adopted the concept of being riskinformed, rather than committing outright to risk-based decisions. Risk-based decisionmaking is particularly important for nuclear waste management and disposal because of 

the long time constants, the inherent complexities of understanding the health effects of 

radiation, and the wide range of alternatives to be compared. 

Risk assessment for nuclear waste activities presents two problems. One is the credibility 

of the risk measure, and the other is the ability to fully understand its meaning. What 

seems to be lacking in many performance studies of high-activity waste disposal or 

storage sites, including the proposed Yucca Mountain repository, is a scientific statement 

of the actual risk involved. Risk is not quantified for the Yucca Mountain repository 

because TSPA-LA does not answer the question, “What is the risk?” Instead, it answers 

the compliance question of whether DOE believes that the regulatory dose standard 

established for the repository has been met. A dose standard is at least once removed from 

a risk standard (Moeller 2008, 2009). 

The nuclear waste community would do well to follow the example of the U.S. commercial 

nuclear power industry and perform and continuously maintain and update PRAs. PRAs 

have become more visible in managing nuclear plant risk than have the federal regulations 

(Garrick and Christie 2002). That is because PRAs are much more meaningful and to 

the point because of their quantification of not only the risk but also the rank order of 

the contributors to risk. Another aspect of this issue that the nuclear waste community 

should follow to improve the transparency of its calculations is to calculate and display 

the risk of different dose levels (probabilities versus different dose levels) in addition to 

the less transparent measure of “probability weighted doses.” This should be easy to do 

because the numbers are the same but how they are displayed is different. This is not to 

suggest that the current dose standard is unacceptable, but only to note that answering 

the question, “What is the risk?” should be part of the process because it provides much 

more information. Furthermore, such a practice would point the way to the possible next 

step in the evolution of a risk standard, if the regulators decide to do so in their quest for 

becoming more risk-informed. 

52 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
Integration 

In addition to its principal function of providing estimates of postclosure performance 

over very long periods of time, TSPA-LA served an important beneficial role as technical 

integrator of a vast store of knowledge and data describing repository characteristics.31 

A major scientific and computational challenge in assessing postclosure performance 

was and is modeling many dynamic and tightly coupled thermo-hydro-mechanicalchemical-radiological phenomena in a complex multivariate nonlinear system. Added to 

this complexity are varying degrees and types of uncertainty regarding the natural and 

engineered systems and knowledge gaps that had to be explicitly identified and quantitatively 

represented. TSPA-LA combined approximately 300 models and submodels from diverse 

scientific and engineering disciplines, combined with thousands of input parameters, to 

provide a model-based probabilistic assessment of the repository system’s performance. 

Documentation that demonstrates the acceptability of a repository to the public and policymakers and the compliance of a repository to regulators is called the “safety case.” It includes 

probabilistic risk assessments as well as corroborative information. Performance assessment 

is arguably the most important part of the safety case, but it also can and should have 

important functions during site characterization. Although DOE performed TSPAs early in 

the site characterization process, which the Board commends, its early use of performance 

assessment was largely independent of many key site-characterization activities. 

Performance assessment could have been used to help integrate the work between groups of 

scientists of different disciplines or from different organizations. For example, geochemists 

from one National Laboratory may perform site characterization to learn how the repository 

environment would evolve, while corrosion scientists from another National Laboratory 

may be conducting experiments to determine how various waste package materials would 

degrade in repository environments. 

Thus, performance assessment models can help show the relationships between the 

work of the two disparate groups, as well as the sensitivity and relative importance of key 

environmental variables, e.g., temperature, pH, and corrosion rates. However, at least early 

in the Yucca Mountain program, performance assessment models and methodology were 

developed parallel with site-characterization activities rather than integral with them. Future 

repository programs should use probabilistic performance assessments throughout the life of a 

program to help set priorities among site-characterization activities, i.e., to guide the research 

portfolio. If performance assessment shows that a particular variable or set of related variables 

is unimportant while showing that other variables are important, more management attention, 

funding, and manpower resources could be allocated to the latter set of variables. 

31 The TSPA-LA model and corresponding probabilistic simulation software were accompanied by a large 

volume of documents that described the technical basis for the diverse sets of models and data used and the 

computational methods applied. 

Contributions from the Yucca Mountain Program 53 
Early performance assessments should be directed toward answering, “What is the 

risk?”, rather than attempting to answer whether there is compliance with regulations. 

Regulations can change, and they did change during the course of the Yucca Mountain 

site-characterization and license-preparation phases. The measure of risk changes less, if 

at all. The parameter of “probability weighted dose” should be avoided because it is not 

transparent. The more transparent approach is to determine the probability of receiving 

a specific dose. Eventually, of course, performance assessment results must be cast in 

compliance-related terms. However, this is not necessary early in a repository project and 

may even be counterproductive for allocating resources or communicating with the public 

or policy-makers. 

In the Yucca Mountain program, different analysis and design practices were used for 

different aspects of the waste-management and disposal system. For example, an entirely 

different approach to safety analysis was performed for the period after repository closure 

(postclosure) than for the period before repository closure (preclosure), making it very 

difficult, if not impossible, to optimize throughput and safety between preclosure and 

postclosure. The preclosure risk assessment was not an integrated probabilistic safety 

analysis, although the postclosure risk assessment contained most of the elements of a 

quantitative probabilistic risk assessment. For future repository-development activities, 

the Board recommends that a consistent framework of analysis and design be used for 

all elements of the nuclear waste-management and disposal system, including storing, 

accepting, handling, transporting, processing, emplacing, and aging of the waste and closing 

the repository. During the design of the surface facilities, it became apparent that despite the 

fact that they were only to operate for 100 or so years, their design requirements were based 

on events with very low probabilities of occurring in 100 years—resulting in overdesign. The 

design basis for facilities should be consistent with their term of use. 

Waste forms may change, depending on how the future of nuclear energy evolves. The 

repository and its design should not be deterrents to changes in waste form that may come 

about as a result of more-advanced nuclear fuel cycles or recycling processes. This may not 

be an important issue in the first repository, if its waste capacity is approximately 100,000 

MTHM or less, because of the current inventory and the known associated waste form. 

However, for future repositories, the compatibility of the repository and its design for 

different waste forms likely to exist for the duration of the repository should be assessed. 

Alternatively, if one assumes that the defense legacy waste goes to the first repository, 

subsequent ones may have a more homogeneous body of SNF of only a few generic types 

to deal with for such factors as heat loading, fuel-element dimensions, and transportation 

and handling requirements. 

54 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
Performance Margin Analysis 

Complex performance assessments may be necessary for licensing, but the public and 

policy-makers may not find them easy to understand. The probabilistic performance 

assessment methods and results developed for Yucca Mountain are a state-of-the-art 

achievement and very valuable. They verge on being incomprehensible because of their 

complexity, however, except perhaps to organizations able to afford a large cadre of experts. 

Future repository programs still may have to produce complex performance assessments for 

compliance purposes, but they also must produce more-realistic, less-complex performance 

assessments for nonregulators. As experience with the Yucca Mountain program clearly 

shows, not only the regulators decide the fate of a repository program. The audience for the 

safety case is much broader. 

Reasonable conservatism is a valid approach to addressing questions of compliance with 

risk standards and limits on system performance. However, in complex and highly coupled 

systems, conservatism is not always easy to prove. An assumption that is apparently 

conservative in one context may prove to be nonconservative in a larger context. Some 

assumptions appeared not necessarily to be conservative, while others seemed unrealistically 

conservative. 

Recognizing the many conservatisms in TSPA-LA, DOE also performed a “performance 

margin analysis” (PMA) (SNL 2008d) to evaluate the importance of many explicit and 

implicit conservatisms. The Board believes that performing the PMA was an excellent idea 

and should be repeated in future repository programs. However, the PMA did not go nearly 

far enough—a serious limitation that should not be repeated by future programs. Two 

examples of deficiencies in the PMA follow. 

1. Despite the fact that zircaloy cladding is highly corrosion-resistant in the Yucca 

Mountain environmental conditions that are likely when water would contact the 

cladding, DOE conservatively claimed no credit for zircaloy cladding in TSPA-LA. 

The chief arguments for not taking credit were the uncertainty about the condition 

of the cladding after discharge from the reactor, particularly for high-burnup spent 

fuels, and the belief that taking credit for zircaloy cladding would not reduce dose 

estimates greatly in the first 20,000 years after closure (SNL 2007d: 3). DOE used PMA 

to examine how much taking credit for zircaloy cladding would reduce the estimated 

dose but limited its investigation to the first 20,000 years after repository closure. The 

analysis showed that the presence or absence of cladding would have little effect in the 

first 20,000 years. This is not surprising, because according to DOE analyses, very few 

waste packages would be likely to fail in the 20,000-year period following closure, and 

therefore any protection offered by cladding would not come into play. DOE should 

have tested the value of cladding credit either by simulating a long-enough period that 

Contributions from the Yucca Mountain Program 55 
substantial numbers of waste packages would fail or by running separate “one-off ” 

cases in which waste packages are assumed to all fail at one time, and then measuring 

the difference in risk versus time as a function of waste package failure time. Future 

repository programs where the EBS has an important function should do the same. 

2. Questions such as, “How important is the waste package?” “How important is the drip 

shield?” and “How important is the unsaturated zone beneath the repository?” are 

obvious ones. The answers to such questions help in understanding how the various 

components of a proposed repository function together as well as the degree of 

defense-in-depth and barrier redundancy in the repository. Although DOE recognized 

the importance of such questions and carried out performance assessment studies 

a decade ago to address them, the PMA did not address them. Future repository 

programs should address these questions, e.g., by running one-off cases. 

56 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
4. CONTriBUTiONS frOM 

ThE ExPEriENCES Of 

OThEr PrOGrAMS 

4.1. LEArNiNG frOM OThEr PrOGrAMS 

Other countries are placing an increasingly high priority on the long-term management 

and ultimate disposition of high-activity wastes from commercial nuclear power generation 

and from defense activities. A strong international consensus has emerged that deep 

geologic disposal is feasible and that it is the preferable mode of disposing of such wastes 

(Sowder 2010). A broad range of approaches toward siting and developing deep geologic 

repositories is being pursued by national programs. Each program takes into consideration 

the operational needs, geology, and socioeconomic circumstances that are specific to the 

country in which the repository would be located. As discussed in the following paragraphs, 

there are many technical differences among the programs and some significant similarities. 

The United States can learn from both. 

4.2. DEEP GEOLOGiC rEPOSiTOrY CONCEPTS 

Many nations with nuclear power plants have active repository development programs. The 

geologic media in which they are developing repository concepts are discussed briefly below. 

Crystalline rock is an inexact term used here to denote intrusive igneous and metamorphic 

rocks composed of well-defined contiguous mineral crystals. The mineralogy is variable. 

Examples are granite, gabbro, diorite, gneiss, and migmatite. Crystalline rock is being 

considered or investigated as a geologic medium for repository development by China, 

Finland, Japan, Korea, Spain, and Sweden.32 Finland and Sweden have the most advanced 

programs, with projected dates to begin repository operations of 2020 and 2025, respectively 

(NWTRB 2009b). Both Finland and Sweden propose to load waste into copper waste 

packages and emplace the packages surrounded by bentonite buffer in holes bored into 

the host crystalline rock. Access drifts would be back-filled with a bentonite-sand mixture. 

Fracture-free crystalline rock has low permeability to the flow of water. However, crystalline 

32Granite also has been considered a repository medium by Canada, France, Switzerland, and the United 

States. Another igneous rock, basalt, an extrusive volcanic rock that generally lacks extensive crystallization, was investigated as a potential repository host rock in the United States during the 1970s and 1980s. 

Basalt was of interest because it typically has low primary interconnected porosity and permeability. 

However fracture zones, rubble zones, the tops of basalt flows, and tubes in basalt flows all can have high 

permeability. Borehole studies in basalt at the Hanford site in Washington found very high temperatures 

and highly unstable stress regimes at depth. Both of these conditions would pose significant challenges to 

repository development in that particular geologic setting. 

Contributions from the Experiences of Other Programs 57 
rock is commonly fractured in nature, and fractures may have high permeability. Moreover, 

mining operations typically create fractures around excavations. 

Argillite is a compacted, fine-grained sedimentary rock that contains clay as a major 

constituent. France, Belgium, and Switzerland are considering argillaceous rock as the 

host rock for a potential repository. Argillaceous rock can have the following advantageous 

characteristics: large homogeneous deposits, low permeability, and a tendency for cavities or 

fractures to close via plastic flow (creep) or swelling. In addition, argillaceous rock can have 

high sorption capacity for some radionuclides. Argillites also tend to be reducing because 

of the presence of organic matter. Of the nations contemplating repositories in clay, France 

has the earliest planned date for beginning repository operations: 2025. Other countries 

considering repositories in clay either have not set a date for beginning operations or expect 

to begin operations in the 2040s or later. 

Salt is a sedimentary rock formed by evaporation. Salt (chiefly halite) in domes or in bedded 

formations has been investigated intensively by Germany and the United States for its 

suitability to host repositories. Salt has low permeability. The geologic persistence of salt also 

indicates a lack of groundwater flow because the salt would have dissolved if there were flow 

through the system. In addition, like weakly indurated clays, salt slowly flows, or creeps, 

under lithostatic pressure to close any fractures or voids that may have been caused by 

construction or emplacement activities in the salt. 

The Roles of the Engineered Barrier System and the Natural System 

Since at least the late 1970s, approaches to the long-term management of high-activity waste 

have adopted a “systems view” (IRG 1978). What counts is the performance of the entire 

repository system regardless of how that performance was allocated among the various 

natural and engineered barriers. In some countries, such as Finland, Sweden, and possibly 

Canada and Japan, the engineered system is mostly responsible for isolating and containing 

the waste. In others, such as France, Belgium, and Switzerland, the bulk of the performance 

can be attributed to the clay natural barrier. Similarly, in Germany and at WIPP, the bulk of 

the performance is attributed to the salt natural barrier. 

As discussed in subsection 3.1, at Yucca Mountain, the principal role of the natural system 

is to provide an environment in which the EBS can fulfill its role of delaying radionuclide 

release for a very long time and ensuring that release rates are low. Repositories in 

crystalline rock appear to have a similar relationship between the EBS and the natural 

system. However, designs of the EBS for the two most advanced repositories, those 

of Sweden and Finland, are much different from that of Yucca Mountain and rely on 

different mechanisms to accomplish their principal role. The Swedish and Finnish waste 

packages are made of copper, which is thermodynamically unable to corrode in dissolved58 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
oxygen-free water.33 In addition, the waste packages are surrounded by swelling clay. Over 

time, water that contacts the clay will cause it to swell, greatly retarding the flow of water 

to or from the waste packages.

 The relationship between the EBS and the natural system is different for repositories in salt 

or weakly indurated clay, however. In these cases, the natural system assumes the principal 

safety burden because of its very low permeability and deformability. The EBS still has two 

important roles, however. One is to contain the waste while it is being transported into the 

repository, while the repository is still open, and while the waste is being transported out of 

the repository, if it is retrieved. The other is to compensate for excavation by plugging drifts, 

ramps, shafts, and holes to ensure that they are not fast pathways for radionuclide releases. 

Regardless of the geologic medium, therefore, the EBS is important. 

4.3. TEChNiCAL fACTOrS AND APPrOAChES COMMON TO MANY 

hiGh-ACTiviTY WASTE PrOGrAMS 

Experimental approaches at one site can result in beneficial transfer of knowledge to another 

site even for different geologic media. Following is a discussion of the technical experiences 

and approaches of different countries that may be transferable among waste disposal 

programs worldwide. 

Underground Research Laboratories 

Surface drilling can provide information on the extent, thickness, and lithology of strata that 

show promise for a deep geologic repository. Core samples can help determine the physical 

and chemical properties of the rock and the fluids it contains at a small scale, which permits 

further evaluation of the potential suitability of a site. However, core samples often do not 

preserve significant rock heterogeneities, including fractures and voids. Consequently, full 

evaluation of a site requires “getting underground” to confirm drilling results, to determine 

physical and chemical properties under in situ conditions, and to perform studies at or near 

full-scale and over longer distances or larger rock volumes than is feasible with drill holes. 

Engineers also can develop and test equipment and construction methods at or near full 

scale in underground research laboratories (URLs). 

Countries that have or have had URLs include Belgium (clay), Canada (granite), Finland 

(crystalline rock), France (clay), Germany (salt), Japan (clay and granite), Sweden (granite), 

Switzerland (clay and granite), and the United States (granite, salt, tuff, basalt). 

33 That copper is thermodynamically unable to corrode in pure, dissolved-oxygen-free water is disputed by 

two researchers at the Swedish Royal Institute of Technology (SNCNW 2010). 

Contributions from the Experiences of Other Programs 59 
Yucca Mountain’s 5-mile Exploratory Studies Facility tunnel and 1.6-mile Enhanced 

Characterization of the Repository Block (ECRB) drift proved the value of getting 

underground for conducting scientific and engineering tests and measurements and for 

increasing confidence in repository performance estimates. The ECRB was especially 

important in improving fundamental understanding of the site because it allowed 

characterizations and studies in the area in which the waste would be emplaced. 

The experience of other countries with URLs also reinforces the value of underground 

exploration. For example, German and French researchers carried out a large-scale thermalhydraulic-mechanical heating test in the Opalinus clay at the Mont Terri URL in Switzerland 

(GRS 2007). The test was similar in many ways to heater tests conducted at Yucca Mountain 

(Tsang and Birkholzer 1997). Underground heater tests would have been infeasible without 

subsurface accessibility. Underground tests and experiments are necessary to understand 

interactions between the waste characteristics and the near-field geology disturbed first by 

construction and then by the heat generated by the waste. 

Experimental work on the effects of temperature on salt has been carried out at WIPP 

in New Mexico (Munson 1990), the Asse salt mine in Germany (Rothfuchs 2004), and a 

salt mine in Lyons, Kansas (Buchanan 1989). Surface and underground exploration and 

characterization of salt were carried out at WIPP, at the Lyons salt mine, and at Gorleben 

in Germany. As with potential repository sites in tuff and clay, information gathered from 

boreholes can reveal whether a site is promising, but extensive underground exploration, 

characterization, and in situ experimentation are needed to evaluate the suitability of a site 

and to obtain the information necessary to model its short-term and long-term behavior. 

Underground work was coupled with aboveground laboratory studies carried out in 

the United States on waste form leaching and dissolution in brines and in Germany on 

corrosion of potential waste package materials in brines. 

Several URLs in crystalline rock have operated over the years. Construction began on the 

Äspö Hard Rock Laboratory in Oskarshamn, Sweden, in 1990 to replace the underground 

laboratory at the Stripa mine (in central Sweden, about 150 km west of Stockholm). 

The Äspö Hard Rock Laboratory began operation in 1995 and continues to operate. 

The laboratory at the Stripa mine operated between 1976 and 1992. Construction of the 

ONKALO URL in Olkiluoto, Finland, began in 2004 and reached a final depth of 350 m 

in 2010. It succeeds the Olkiluoto Research Tunnel, which began operation in 1992. Other 

laboratories operating in granite are in Japan and Switzerland (Grimsel). Laboratories in 

granite no longer operating are in Canada (Whiteshell), France (Fanay-Augères), and the 

United States (Climax) (EDRAM 2008). 

International cooperation at the Stripa, Whiteshell, and Grimsel laboratories was extensive. 

International cooperation at the Äspö Hard Rock Laboratory also has been extensive, 

60 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
involving many nations. Finland and Sweden are strongly motivated to cooperate because 

they share key features of repository design and site geology. The cooperation has resulted in 

sharing ideas, communicating results, and lowering research costs through shared funding 

and avoidance of unnecessary repetition. Future U.S. repository programs will benefit from 

cooperative international research, regardless of lithology. 

Prototyping 

The conceptual design for the repository in France includes many novel material and 

equipment items for containing or emplacing the waste. They include seals and plugs for 

shafts and access drifts and the machinery for placing the seals and plugs; the waste package 

itself; and the equipment for sealing the closure lid onto the waste package after the package 

is loaded with waste, for inserting the waste packages in their emplacement sleeves, and 

for placing backfill (a bentonite-based material) in the drifts used to access the wasteemplacement sleeves. 

Because operation of the repository is only 15 years away, engineers at the French repository 

already have begun a prototype program. Full-scale equipment for pushing waste packages 

into the emplacement sleeve has been developed and is being tested. Clearly, all of the 

novel equipment items will need to be developed and tested before the repository begins 

operation. The French repository is being designed for disposing of vitrified waste. 

The designs for the repositories in Finland and Sweden also have several novel engineered 

components for containing or emplacing the waste. They include the copper waste package 

used for direct disposal of spent fuel; equipment for sealing the closure lid onto the waste 

package after the package is loaded with spent fuel; machinery for transporting the packages 

underground and emplacing them; rings of compressed bentonite; and machinery for 

making and emplacing the bentonite rings. 

An example of the extensive prototyping developed by the Swedish program was the design 

and manufacture of a solid copper container with a wall thickness of 50 mm. Engineers 

in the Swedish disposal program realized early that the lids would have to be attached to 

the waste package shell by welding to ensure long-term leak-tightness. Although methods 

existed to weld copper, making 50-mm-thick welds in copper was an unusual challenge. 

Accordingly, the Swedish nuclear-waste program management decided in the mid-1990s 

to build a full-scale prototyping facility to test, develop, and perfect welding methods for 

sealing waste packages. The facility, the Canister Laboratory, opened in 1998 in Oskarshamn, 

Sweden. The first welding method used was electron beam welding, an existing method but 

one that had not been used to make thick copper welds. At the laboratory, the method was 

used to join full-scale waste packages and lids. The method was developed successfully but 

required precise control of parameters for reproducible, acceptable welds. Nondestructive 

Contributions from the Experiences of Other Programs 61 
methods for examining weld quality were developed at the same time. In the 1990s, 

Swedish engineers also began working at the laboratory level with The Welding Institute 

in Cambridge, England, to develop an alternative method for sealing waste packages based 

on friction stir welding. Following its successful development, equipment for sealing waste 

packages at full scale by friction stir welding was installed at the Canister Laboratory, where 

it was perfected and then chosen in place of electron beam welding. 

Over the same period, a full-scale shielded waste package deposition machine was designed, 

constructed, and deployed at depth in the Äspö Hard Rock Laboratory using full-scale waste 

packages filled with surrogate (nonradioactive) waste. In addition, engineers in the Swedish 

program developed full-scale equipment for manufacturing the bentonite rings that will be 

placed around emplaced waste packages, and they also carried out full-scale experiments for 

placing and handling the rings. 

Each of these prototyping activities was critical for engendering confidence that successful 

emplacement and permanent disposal of nuclear waste generated by the Swedish reactor 

program could be accomplished. The Swedish program has set an excellent example of 

prototyping, one that the future U.S. program should emulate. 

Thermal Management 

High-activity waste generates heat as it decays, and the effect of that heat on the host 

rock must be determined. This requires knowledge of the thermo-physical properties of 

the rock as well as carefully developed and sophisticated mathematical models based on 

first principles of heat transfer. If changes in chemistry or mineralogy over the range of 

expected temperatures are potentially significant, then those processes must be included 

in the models. Thus, all repository programs limit the maximum temperature that the host 

rock will encounter. The limit can be met by aging the waste before emplacing it, placing 

waste packages farther apart, providing better heat transfer in the repository, or by other 

engineering means. 

Temperature limits also must be set for clay-based buffers. Because a future U.S. repository 

could include clay formations or clay-based buffers, the U.S. program would benefit from 

understanding the thermal modeling of other programs, from examining the designs of 

other programs to achieve thermal management goals, and from learning the rationale 

behind the engineering approaches to achieving the thermal goals. If the host rock of a 

future U.S. repository is clay, the thermal modeling and management work of other clay 

programs would be directly useful. 

Salt has a higher thermal conductivity than clay and may contain inclusions of brine that can 

migrate from regions of lower temperature to regions of higher temperature. In addition, 

62 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
the creep rate of salt increases with temperature. (The creep rate of clay depends in part on 

the degree of induration of the clay.) The effect of heat generated by the waste on the specific 

salt formation under consideration must be determined. Extensive thermal modeling of 

waste emplaced in salt has been performed in both Germany and the United States and is 

continuing in Germany. If salt is considered for a future U.S. repository program, approaches 

to thermal management in other salt programs should be monitored carefully. 

Whatever host rock is chosen for a future U.S. repository, the thermal modeling and 

management work of the United States and other countries will be of value. 

Reducing versus Oxidizing Environments 

The proposed Yucca Mountain repository is the only one in which the repository bulk 

environment would be always oxidizing. This is due to continuous gas exchange with the 

atmosphere. The repositories of other programs also would have a period during which 

the environment would be oxidizing, but the period would be brief—a few hundred years 

or less—and would occur immediately after repository closure. The cause of the brief 

oxidizing period for repositories of other programs is the oxygen in the air left behind in 

drifts at the time of repository closure, oxygen entrapped during placement of buffer or 

backfill, atmospheric oxygen that had diffused into host-rock fractures during the repository 

preclosure period, and dissolved oxygen in porewater due to contact between the porewater 

and atmospheric oxygen during the preclosure period. The time required to consume the 

oxygen, e.g., by reaction with engineered components of the system or the geochemical 

environment, determines the duration of the oxidizing period. The environment becomes 

and remains reducing following consumption of the oxygen. 

Although repositories in permanently oxidizing environments certainly are possible, 

emplacement of high-activity waste in reducing environments generally has three important 

advantages: (1) solubilities of most radionuclides are lower; (2) corrosion rates of metallic 

engineered components are slower and can approach zero; and (3) the UO2

 of spent fuel is 

stable in a reducing environment but converts to less-dense U2

O3 in oxidizing environments. 

Because these advantages enhance long-term isolation of the waste from the human 

environment, future U.S. repository developers should ensure that repositories in reducing 

environments are considered. 

Undisturbed in situ salt without brine pockets or significant impurities contains very 

little water, typically less than 1 percent (Roedder and Bassett 1980), and the water is 

salt-saturated brine. Water moves through the salt at slow rates because of the salt’s low 

permeability. Brine can be highly corrosive. 

Contributions from the Experiences of Other Programs 63 
As in repositories in clay or crystalline rock, the environment in salt repositories 

immediately after repository closure will be oxidizing. That oxygen would be consumed 

within a few hundred years after repository closure by reaction with iron-based structural 

materials and other materials. Because of the presence of metals, i.e., structural materials, 

the environment would become reducing following the consumption of free oxygen. 

Use of Swelling Clay 

Every repository program has investigated swelling clay (e.g., bentonite) as a major 

component of buffers, backfills, seals, or plugs. Buffers are packed around waste packages 

to retard radionuclide transport by slowing or stopping the flow of water to and from the 

packages and to provide mechanical support. Backfill is placed around the buffers or in 

access drifts when sections of a repository are being closed. Seals and plugs are used to 

prevent fluid flow through smaller openings. 

Because swelling clay may play an important role in any future U.S. repository, future U.S. 

programs should include awareness of, and become involved in, cooperative international 

research efforts on buffers, backfills, and other uses of swelling clays. 

Integrated Waste-Management Systems 

The waste-management system in the United States is a highly complex system consisting 

now of waste acceptance, handling, transportation, and at-reactor storage. Eventually, 

the system also may include functions and facilities for repackaging, centralized storage, 

recycling, and final disposal. When fully developed, the U.S. waste-management system 

arguably will be the most complex because of the size and geographic dispersion of the 

nuclear power industry and the large amount of legacy waste requiring management and 

ultimate disposal. Today, however, other countries operate waste-management systems that 

are more complex, more complete, and more integrated than that of the United States. 

France has been operating the most highly integrated, most advanced, and most complex 

national nuclear waste-management system in the world for decades. France has 58 

operating nuclear power plants, second only to the 104 operating nuclear power plants in 

the United States. In contrast to U.S. nuclear power plants, French nuclear power plants have 

only a relatively few years of on-site storage capacity for SNF. After a cooling period on site, 

SNF is shipped from a reactor to a centralized storage facility located at the AREVA plant in 

La Hague. There, the SNF is either stored temporarily or reprocessed. 

The French waste-management program includes a complex system of at-reactor and 

centralized storage; transportation by road, rail, and water; reprocessing; and fuel 

manufacturing from plutonium recovered by reprocessing. In addition to dealing with 

all of the spent fuel produced in France, the French waste-management program also 

64 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
receives, stores temporarily, and reprocesses spent fuel from other nations and ships back 

products from reprocessing to them. The only element of a waste-management system 

missing at the present from the French system—as it is from the waste-management 

systems of all countries—is a deep geologic repository for permanent disposal of highactivity nuclear waste. 

Like France, Sweden also has a highly integrated, advanced, and complex wastemanagement system that operates efficiently. The Swedish waste-management system is 

somewhat less complex than France’s, because Sweden has fewer operating reactors (10 

versus 58 in France) and because it does not include a reprocessing facility, does not have 

significant shipments of waste to or from other countries, and can depend primarily on 

transport by sea. Like France and unlike the United States, Sweden does not have extensive 

storage capabilities at the reactor sites. Instead, SNF is shipped to a large, centralized interim 

storage facility at Oskarshamn, where it awaits final disposition. 

In contrast to France and Sweden, the United States has relatively little experience with 

transportation of commercial SNF and does not have either a centralized storage facility 

or a reprocessing facility for commercial SNF. There have been several shipments of spent 

fuel from research reactors, but each of these shipments has been treated as a one-of-a-kind 

event. The U.S. Navy does have a finely tuned, tightly integrated waste-management system 

for its SNF that includes a centralized storage facility at the Idaho National Laboratory (INL) 

and a rail-based transportation system for bringing spent naval fuel to INL. 

OCRWM recognized the complexities of the integrated waste-management system that 

it would need to develop and had a program for planning, constructing, and operating 

an integrated system for managing commercial SNF. The results of that planning are well 

documented, although the thinking behind the planning is less well documented. Much of 

the undocumented experience of planning a waste-management system for commercial 

spent fuel in the United States may be lost permanently without action. (See “The Current 

Technical Experience Base” section in the next chapter for a recommendation for capturing 

this experience.) The French experience is likely to be available, as well as the experience of 

other countries operating complex waste-management systems. Those programs, the U.S. 

Navy program, and their histories, should serve as valuable resources for informing future 

U.S. programs. 

4.4. CONTriBUTiON Of MULTiNATiONAL AGENCiES TO rEPOSiTOrY 

DEvELOPMENT PrOGrAMS 

Two multinational organizations, the International Atomic Energy Agency and the 

Nuclear Energy Agency, have played important roles in the development of radioactive 

waste-management programs in the United States and abroad. OCRWM and the Nuclear 

Contributions from the Experiences of Other Programs 65 
Regulatory Commission have been active in both organizations, although OCRWM’s 

participation has been limited because the oxidizing tuff of Yucca Mountain differs from the 

reducing geologic media of repository programs of all other countries with active repository 

programs. If the United States redirects its efforts away from the Yucca Mountain program, 

both international organizations are likely to be still more influential on the U.S. waste 

management and disposal program in the future. In particular, many of their contributions 

will be viewed through eyes not constrained by the programmatic interests specific to the 

Yucca Mountain program. 

International Atomic Energy Agency (IAEA) 

The IAEA was set up in 1957 as an autonomous organization reporting to the General 

Assembly and Security Council of the United Nations. The agency works with its member 

states and multiple partners worldwide to promote peaceful nuclear technologies. Guided by 

the interests and needs of member states, the IAEA’s mission is threefold: safety and security, 

science and technology, and safeguards and verification. 

Until relatively recently, most of the effort of the Nuclear Fuel Cycle Division in IAEA’s 

Department of Nuclear Energy was directed toward transferring information and 

technology for managing low- and intermediate-level nuclear materials, including medical 

isotopes and decommissioning waste. Greater attention is being paid now to high-level 

radioactive waste and spent nuclear fuel. The division, for example, sponsors training 

seminars that are attended by leaders of nuclear waste-management organizations from 

countries that are only just beginning to consider how to implement geologic disposal. 

Most of the division’s energy and resources are directed toward the publication of 

TECDOCs (technical documents). The Division published or will soon publish 

TECDOCs addressing, among other things, the use of anthropogenic analogs, the 

technical implications of retrievability for geologic repositories, the applications of 

numerical modeling, and factors affecting public and political acceptance of disposal 

facilities. These TECDOCs are an important resource for nations with modest wastemanagement programs. For nations with larger programs, the TECDOCs can provide 

a vehicle for demonstrating that approaches taken by a particular national program are 

consistent with international practice and opinion. 

The Division of Radiation, Transport, and Waste Safety within the IAEA’s Department 

of Nuclear Safety and Security publishes three different types of safety standards. 

Safety Fundamentals are policy documents that state the basic objectives, concepts, and 

principles involved in ensuring radiological protection and safety. Safety Requirements are 

derived from the Safety Fundamentals and are written as “shall” statements. They may be 

used as a basis for national regulations. Safety Guides contain recommendations on how 

66 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
to meet the requirements. They use “should” statements and are based on international 

experience. In 2006, for example, a Safety Requirements document for geologic disposal 

was released (IAEA 2006). 

The IAEA’s Waste Safety Standards Committee oversees the process for preparing all safety 

standards. The IAEA staff, exercising considerable discretion, invites experts to work 

on each standard. A standard may be revised a dozen times before it is sent to member 

states for review. Comments received must be addressed fully because a standard cannot 

be issued unless there is full consensus among member states. Consequently, standards 

typically represent the “lowest common denominator” position, which is open to multiple 

interpretations. In particular, the standard will never directly contradict a stance taken by 

a member state, especially those with advanced nuclear power programs. Nonetheless, the 

document can significantly affect regulatory policies in member states. Increasingly, there 

seems to be a desire on the part of national authorities to promulgate regulatory standards 

that appear to be “harmonized” with the standards established by other authorities. 

Nuclear Energy Agency (NEA) 

The NEA is a specialized agency within the Organization for Economic Cooperation and 

Development, an intergovernmental body whose membership includes 33 developed 

countries committed to democracy and the market economy. The mission of the 

NEA is to assist its member countries in maintaining and further developing, through 

international cooperation, the scientific, technological, and legal bases required for the safe, 

environmentally friendly, and economical use of nuclear energy for peaceful purposes. 

To achieve this, the NEA works as a forum for sharing information and experience and 

promoting international cooperation, a center of excellence that helps member countries to 

pool and maintain their technical expertise, and a vehicle for facilitating policy analyses and 

developing consensus based on its technical work. 

The NEA’s work in radioactive waste management is overseen by its Radioactive Waste 

Management Committee and is carried out by several subsidiary bodies, including the 

Forum on Stakeholder Confidence (FSC), the Integration Group for the Safety Case 

(IGSC), the Regulators’ Forum, and the Advisory Bodies to Government. Over the last 

decade, in particular, these bodies have been extremely active, not only providing venues 

for discussions across national programs but also publishing a voluminous record of 

deliberations, analyses, and peer reviews. Collectively, these works often represent the stateof-the-art thinking about issues that are likely to confront a redirected U.S. program. 

For example, for the last 10 years, the FSC has been focusing on efforts in Canada, France, 

Finland, and Belgium to bring interested and affected parties more meaningfully into the 

work of national programs. The record it has produced will provide consensus insights for a 

Contributions from the Experiences of Other Programs 67 
redirected U.S. program. Further, the IGSC has done very important thinking about what a 

safety case should look like and how a national program might advance it (NEA 2008). The 

IGSC has produced noteworthy technical documents as well. (See http://www.oecd-nea.org/ 

rwm/igsc/.) A redirected U.S. program would benefit from NEA’s work, which is innovative 

and, in many respects, path-breaking. 

Importance of Cooperation

 Nations with waste disposal programs have a high degree of cooperation and many 

joint research programs. For example, under the auspices of the Nuclear Energy Agency, 

countries with interest in repositories located in clay formed a working group in 1990 on 

argillaceous media, informally known as the “Clay Club,” to share experiences and ideas. The 

Clay Club includes Belgium, Canada, France, Germany, Hungary, Japan, Spain, Switzerland, 

the United Kingdom, and the United States. Members share data on clay properties and 

behavior, on methods of testing in clay media, and on specific features, events, and processes 

specific to long-term disposal of high-activity waste in clay media. Argillaceous rocks 

may be among the media considered a potential host medium for future U.S. repository 

programs, and the United States will benefit from its association and cooperation with other 

countries considering clay. 

Many nations with repository programs have independent governmental entities having 

oversight roles similar to those of the Board, including France, Germany, Japan, Sweden, 

Switzerland, and the United Kingdom. The Board cooperates with those entities through an 

informal organization, the Advisory Bodies to Government (ABG), which was established 

in early 2004 under the auspices of the NEA. The ABG’s purpose is to provide a forum 

for organizations similar to the Board to meet and exchange information and to share 

experiences in their successes and setbacks in accomplishing their assigned missions. 

68 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
5. MOviNG fOrWArD
 

The Board believes that keeping a focus on a permanent solution is critical regardless 

of what interim measures for managing high-activity waste are charted. Among the 

reasons are (1) a permanent solution is critical to building public confidence that 

there is a way of isolating nuclear waste radioactivity from the biosphere to acceptable 

levels; (2) given the long duration of the hazard of high-activity waste, undue delay in 

implementing a permanent solution could make tenuous a concept of waste management 

dependent on institutional stability; (3) experience to date has indicated that deploying 

a permanent solution to isolating high-activity waste could take decades; and (4) there is 

an international consensus that a permanent solution to high-activity waste isolation is 

feasible via geologic disposal. These reasons are believed to be compelling for a focused 

effort to implement a permanent solution for disposing of high-activity waste. Although 

the problems of deployment involve many factors, including institutional and political 

considerations, this report has focused primarily on the technical issues associated with 

implementing a permanent solution and technical lessons learned from the experiences of 

the Yucca Mountain program and other programs. 

The Yucca Mountain program has contributed significantly to the technical knowledge 

base for developing a geologic disposal facility for high-activity waste. As discussed in 

chapter 3 of this report, major advances were made in assessing the performance of 

engineered barriers and the natural system associated with geologic disposal. Advances 

were made in modeling water flow in unsaturated fractured rock in semiarid zones, 

understanding the role of matrix diffusion in transporting radionuclides, and using 

analog information as evidence for assessing hydrogeologic behavior of geologic units. 

Chapter 3 also discusses the important use of systems analysis tools, such as the total 

system simulation model and quantitative probabilistic risk assessment, to ensure that the 

repository is integrated with the balance of the waste-management system and to portray 

the risk of the repository over time. The Yucca Mountain program developed considerable 

data, methodology, and evidence to indicate the technical feasibility of isolating highactivity waste in an unsaturated, oxidizing environment. 

Other programs, both in the United States and abroad, also have contributed significantly 

to the technical knowledge base for geologic disposal, as discussed in chapter 4. Together, 

Moving Forward 69 
the knowledge gained in the Yucca Mountain program on tuff as a repository medium in 

an oxidizing environment and the knowledge gained in other programs in other geologic 

media and reducing environments are a very strong technical base for moving forward with 

geologic disposal in the United States. 

The worldwide experience to date strongly suggests that the steps necessary to move forward 

technically in an efficient and cost-effective manner are the following: 

(1) ensuring that the Yucca Mountain and international knowledge and experience base are 

available and accessible to future U.S. repository developers 

(2) developing an experience-based site-selection and site-characterization process that 

incorporates systems-analysis methodology 

(3) characterizing existing and new waste forms in concert with existing inventories of highactivity waste 

(4) developing organizational and project plans for site selection and characterization and 

for design, licensing, construction, and operation of a geologic disposal facility for highactivity waste and integrating the plans with the entire waste-management system. 

ENSUriNG ThE AvAiLABiLiTY AND ACCESSiBiLiTY Of ThE CUrrENT 

TEChNiCAL ExPEriENCE BASE 

There are several decades of experience involving tens of millions of person-hours dedicated 

to developing geologic disposal as a permanent solution for isolating nuclear waste from the 

biosphere. This has come about because of the international consensus that geologic disposal 

is at least a necessary part of the solution for managing high-activity waste. The experience 

base involves different geologic media, different concepts for engineered barrier systems, 

different waste forms, and extensive use of performance assessments, including probabilistic 

risk assessments. The knowledge base for geologic disposal has increased immensely in the 

last two decades. 

Much (but not all; see below) of the experience base of the last several decades is available 

in the form of technical papers and technical reports. Highly detailed technical information, 

such as detailed engineering drawings and detailed descriptions of experimental apparatus, 

tends to be less available. Detailed drawings are on the Licensing Support Network (LSN), 

but the legibility of the drawings often is poor. Obtaining original (paper) drawings is a 

laborious process. One would not expect that such detailed information would be sought 

early in the process of moving forward, however. The action needed to begin moving 

forward is ensuring that relevant technical information is readily available and accessible. 

Because many of the programs and models were run on hardware that may not be readily 

70 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
available in a few years, DOE should preserve not only the software (computer codes) but 

also the hardware, without which the codes cannot be run unless completely rewritten (a 

huge and unnecessary undertaking). 

Much of the Yucca Mountain experience base is currently available and accessible through 

the LSN. Although the extreme redundancy of data in the LSN limits its value, a key first 

step would be to ensure that the LSN remains available. There is nothing comparable 

to the LSN for the international experience base. Accessing the information of other 

countries would entail international cooperation, such as discussed in chapter 4. The first 

steps of any new program should be to forge strong bonds with the waste-management 

and disposal programs of other countries, both directly and through the auspices of the 

IAEA and the NEA. 

Some of the bases for technical decisions can be found in presentations made by DOE 

managers and M&O and National Laboratory technical personnel to the Nuclear Waste 

Technical Review Board and to the Nuclear Regulatory Commission’s now-defunct Advisory 

Committee on Nuclear Waste (ACNW). The Board has been holding public meetings since 

1989. Overheads and transcriptions of presentations made at the meetings are available 

at the Board’s Web site, www.nwtrb.gov. The ACNW held meetings from June 1988 until 

May 2008. Many of the overheads and transcripts of presentations at those meetings can be 

obtained from the Nuclear Regulatory Commission’s Web site, www.nrc.gov. 

Despite the information in TMRB34 minutes, the NWTRB and Nuclear Regulatory 

Commission Web sites, and other available program documents, answers to the questions 

about the rationale underlying technical decisions still remain unavailable. This is 

unfortunate from a lessons-learned viewpoint, because understanding the reasoning behind 

Yucca Mountain decisions would help future repository developers emulate past good 

decisions and prevent repeating past mistakes and poor decisions. Information about the 

decisions resides with former senior OCRWM personnel, DOE contractor personnel, and 

USGS and National Laboratory personnel formerly associated with the program. Very few 

are working in the field of high-activity waste management today. Locating them soon and 

obtaining their retrospective views and insights could be very helpful to future developers. 

SiTE SELECTiON AND ChArACTEriZATiON 

The Board came into existence in 1987 at the same time that Yucca Mountain was 

designated as the only site to be characterized for hosting a geologic repository. Ten years 

of characterizing Yucca Mountain for a repository already had taken place by 1987. Thus, 

the Board was not involved in site selection or in the first decade of site characterization. 

34The Technical Management Review Board (TMRB) was a panel of senior technical managers of the M&O 

contractor located in Las Vegas (BSC 2002). 

Moving Forward 71 
The Board believes, however, that probabilistic risk assessments were not used in the siteselection process, partly because EBS designs for the various sites under consideration had 

not been developed. The Board believes that using PRAs to compare sites is now feasible 

because EBS designs appropriate for various geologic media have been developed by many 

programs. The Board notes, however, that the collective Yucca Mountain, WIPP, and 

international experience to date strongly suggests that repositories can be developed in many 

geologic media. Deciding factors for site selection, therefore, may well be nontechnical. 

Nonetheless, the Board recommends that PRA be used as part of the site-selection process and 

during site characterization. The level of complexity of PRAs developed to assist site selection 

and characterization should be appropriate for the site-selection and site-characterization 

questions at hand. That is, they should be considerably less complex than PRAs developed 

for licensing purposes. 

ThE WASTE fOrM 

Some of the DOE-owned SNF degrades more rapidly when contacted by water than 

commercial SNF. Depending on the medium for geologic disposal, this suggests that tradeoff 

studies could be performed to assist in determining the relative advantages of treating some 

of the DOE-owned SNF to improve its performance in a geologic environment. Treatments 

considered could include (1) chemically treating the DOE-owned SNF to obtain a more 

resistant waste form; (2) chemically separating the radionuclides and then treating and 

packaging each separated component in a manner commensurate with its risk; and (3) 

repackaging or overpackaging the DOE-owned SNF to delay the time when water reaches 

the waste form. 

Vitrification of liquid waste into a highly stable borosilicate waste form was selected three 

decades ago. There is considerable experience with vitrification at full scale at the Savannah 

River Site, at West Valley, and at the La Hague plant in France and the Sellafield plant in the 

United Kingdom. Research continues on vitrification to improve the percentage of waste 

that can be incorporated into the waste form while maintaining its long-term durability. 

Research also continues on ways to improve processing equipment, increase throughput, 

and reduce overall processing costs. Some U.S. high-activity waste, e.g., vitrified HLW at 

Savannah River, is significantly less hazardous than commercial SNF on a volumetric basis 

or on a per-waste- package basis (see SNL 2008a: Table 6.3.7-3). Treating such wastes more 

aggressively or packaging them more robustly than commercial SNF is treated or packaged 

makes no sense because commercial SNF is the dominant contributor to repository risk. 

Depending on the geologic medium, the waste form can be a critical factor when it comes 

to a permanent solution, such as geologic disposal. The waste form is part of the strategy 

of engineering into the repository an EBS that substantially delays arrival of radionuclides 

72 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
at the natural system, thereby gaining a major benefit from radioactive decay. Planning 

a geologic disposal facility requires extensive total system analysis and trade-off studies 

to determine acceptable and appropriate waste forms and EBS designs for a specific site. 

That is, the waste form can be optimized only on a site-specific basis. As discussed in 

chapter 2, the wide variety of U.S. waste forms compels the United States to choose among 

several alternatives: seek a single disposal system that can accommodate them all; process 

or package the wastes into more-or-less standard forms for disposal; or develop separate 

geologic disposal facilities for different classes of wastes. Current waste-form characteristics 

and inventories should be reexamined, and the issue of the appropriate disposal method for 

each waste form should be addressed. Many previous decisions about multiple repositories, 

waste processing and packaging, and repositories dedicated to classes of wastes were made 

in a Yucca Mountain context. These decisions will have to be made again. Trade-off studies 

may inspire new ideas on waste management, such as one type of geologic disposal for 

most of the waste, e.g., waste that is retrievable, and another type of disposal for waste that 

may involve vitrified waste, less stable spent-fuel assemblies, or even damaged fuel. Such 

wastes may be better suited for other measures, such as deep boreholes, where retrieval may 

be difficult or impossible. Such separation of wastes may allow greater flexibility in siting 

facilities and improved confidence in the performance assessments. 

DEvELOPiNG iNTEGrATED OrGANiZATiONAL AND PrOjECT PLANS 

Lack of integration among various aspects of the Yucca Mountain program is discussed in 

sections 1, 5, and 6 of chapter 3. The relative success of other programs, notably the WIPP 

program and the Swedish program, provides strong evidence that several Yucca Mountain 

program deficiencies could have been prevented if a total integrated systems approach had 

been adopted. 

Perhaps the biggest challenge to moving forward with a permanent solution to managing 

high-activity radioactive waste is developing the right kind of project plan and an 

implementing organization that is capable of adapting as technical needs change from 

primarily scientific to primarily engineering. From the beginning, the organizational 

culture has to be one of actually building something on time and within budget that 

meets all technical specifications and relevant local and federal regulations. At the same 

time, until a site is chosen, characterized, and found suitable, there is no project to 

plan. Site characterization itself is fundamentally a science program, but one that must 

take engineering considerations into account. Scientific activities can be scheduled but 

not scientific results. On the other hand, with the rich worldwide experience base in 

characterizing different geologic media for repositories, the time needed to characterize a 

specific site might be bracketed. In any case, the transition from engineering serving science 

to science serving engineering is not a sharp one. 

Moving Forward 73 
Because site selection, site characterization, and repository engineering are such different 

projects, consideration should be given at the outset to the appropriate skills, organizational 

form, and even institutional form for each project. The Yucca Mountain program was a mix 

of science and engineering, with the resulting conflicts of authority and management of the 

two disciplines. The transition between science and engineering in a first-of-a-kind program 

that involves new knowledge and technologies is sometimes difficult to resolve. Nevertheless, 

the lesson learned is that it is important to establish the point at which the science part of the 

program assumes a supporting role to the engineering. In particular, once the project becomes 

an engineering project, the technical and scientific needs of the project should be driven by what 

it takes to engineer the project to its performance goals. 

The Yucca Mountain program management began to change from a science project to 

an engineering project a few years before the formal recommendation of the site by the 

Secretary of Energy in early 2002. However, the science, although sufficient for the formal 

recommendation, was not sufficient for the documentation and performance assessment 

required for the license. In addition, developing the TSPA-LA itself was treated much more 

as a science project than an engineering one. Whether envisioning and managing the project 

as an engineering one from the very beginning would have resulted in a better outcome is 

a question that deserves to be addressed. The end product is clearly an engineering one, and 

engineering could guide the science even from the beginning of site selection. 

CONCLUDiNG rEMArKS 

As a result of the activities of the Yucca Mountain program and other repository programs 

for high-activity waste over the last several decades, the knowledge base for disposing 

of high-activity waste has grown significantly. Key accomplishments of value to future 

repository development programs include the following: 

•	 submittal of a license application that the Nuclear Regulatory Commission found

acceptable for review 

•	 development of an engineered barrier system design that, according to the license

application, will perform as a significant barrier for 1,000,000 years 

•	 development and application of methods for evaluating the performance of geologic

units involving unsaturated zones in an oxidizing environment 

•	 development of additional evidence that many different geologic media, including

unsaturated tuff in an oxidizing environment, have the potential to host geologic 


repositories
 

•	 substantial evidence that engineering may be used to turn less-than-technicallyoptimal repository sites into better ones 

74 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
•	 establishment of probabilistic risk assessment as the principal method for measuring

the risk of a repository 

•	 trade-off studies on the appropriate waste form, packaging, and geologic media for

various high-activity wastes 

•	 insights on the best institutional form(s) for the various phases of a repository project,

how to transition from one phase to another, and whether a single institutional form 

can be appropriate for all phases. 

Moving Forward 75 

6. rEfErENCES
 

Abraham, ES, Letter to the President Recommending the Yucca Mountain Site, February 14, 

2002 

Ahearne, JF, “Is nuclear waste the Achilles’ heel of the “nuclear renaissance?” (DRAFT), 7/10, 

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84 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
APPENDICES


APPENDix A-1
 

EvOLUTiON Of ThE CONCEPTUAL DESCriPTiON Of ATMOSPhEriC 

DUST AND ThE WASTE-PACKAGE COrrOSiON ENvirONMENT 

The conceptual description of the waste-package corrosion environment that is due to 

the deposition of atmospheric dust on the metal during preclosure ventilation evolved 

considerably over the life of the Yucca Mountain program. What has changed is the 

description of the composition of the dust, what happens to the dust in a chemical reaction 

sense, and the effect of radiolysis. That the dust layer on waste package surfaces is a dynamic 

reacting chemical system with a continual supply of reactants has been known for about 10 

years. Yet today, there is no complete conceptual description of the corrosion environment 

on a waste package’s metal surface. 

The major topics that bear on the evolution of the conceptualization of the corrosion 

environment on a waste package as affected by atmospheric dust are the existence of 

calcium chloride in and on atmospheric dust (Prather 2010); the existence of organic 

matter in and on atmospheric dust (Gelencsér 2004); the reaction of organic matter 

and nitrate in dust that depletes the nitrate content (Peterman 2008); radiolysis effects, 

including gamma radiation of chloride salts producing halogen bubbles within the salt 

(Dubinko et al. 2000); and the radiolysis of moist air producing oxides of nitrogen and 

specifically nitric acid (Tang and Raduescu 2002). Examination of the details of these 

five major topics leads to the conclusion that the corrosion environment as described 

at the time of the License Application Design Selection Report (CRWMS M&O 1999) is 

incomplete. A brief discussion of the five topics follows. 

Calcium chloride in and on atmospheric dust is considered rare from a geologic perspective 

because its natural existence on the surface of the earth occurs at only two places: in 

Antarctica and California (Dunning and Cooper 1969). Dust and its components lofted into 

the atmosphere from the earth’s surface are called primary components. Dust components 

generated by chemical reaction in the atmosphere are called secondary components, and, 

except for the rare situation of Bristol Dry Lake in California (which is actively mined for 

calcium chloride), calcium chloride is the product of the reaction of calcium carbonate 

(calcite) and hydrogen chloride in the atmosphere, as noted by Prather (2010) and Sullivan 

et al. (2007). Calcite is ubiquitous in atmospheric dust as a primary component. 

Appendix A-1 87 
Therefore, it also is possible to conclude that dolomite and hydrogen chloride will react 

and result in the production of magnesium chloride as a secondary component, along with 

calcium chloride. The observation that atmospheric dust contains organic matter is beyond 

question. Books have been published on this topic, and the publications are too numerous to 

cite here. The book by Gelencsér (2004) is an excellent starting point for becoming familiar 

with this topic. 

The hypothesis that organic matter and nitrates can react was put forth in early 2007 

because of the recognition that organic matter is a reducing agent and nitrate is an 

oxidizing agent, and thus these two components can react, resulting in the loss of nitrate 

and organic matter (Garrick 2007). Although the progress of reaction cannot be readily 

predicted at ambient or near-ambient temperatures, the thought at the time was that the 

local corrosion-environment temperature of a waste package in Yucca Mountain could be 

high enough for this reaction to proceed at an observable rate. This turned out to be the 

case, as demonstrated by experiment by Peterman, previously cited, where nitrate loss from 

heated atmospheric dust was reported to occur over a time span of days; minimal loss of 

chloride was observed. This particular experiment was not conducted in exactly the same 

environment expected in a repository: Ambient air prevailed, so the sample was considered 

dry. In a repository, the dust would be subject to a higher-humidity environment after 

closure, and with more water present, the phenomenon of acid-gas devolatilization could 

occur. Acid-gas devolatilization is a process in which hydrogen-chloride gas is lost from an 

aqueous phase. If this phenomenon were to occur, the corrosion environment eventually 

would experience a low chloride concentration. However, no experiments have been 

reported that directly demonstrate this phenomenon, and conclusions have been reached 

through indirect observations. 

Radiolysis effects on the dust-humid air environment on waste package surfaces have 

not been considered, but well known is that gamma radiation can break chemical bonds, 

producing myriad chemical species, including free radicals. The effect of radiolysis on 

uranium oxide dissolution has been noted, where water radiolysis produces oxidizing and 

reducing species, including radicals (e.g., OH–, O2

–, HO2–, e–

aq, H+) and molecular species at 

concentrations that depend on the type of radiation (a or b-g) and the dose deposited in the 

water interface (redox imbalance with the environment), and thus enhances the dissolution 

of the oxide layer protecting the waste package (Frizon et al. 2009). Similar effects may occur 

for any oxide. In the case of the exposure of alkali halide salts to gamma radiation, halogen 

bubbles have been observed, as reported by Dubinko (2000). The effect of radiolysis was 

noted in the Climax Spent Fuel Test where it was observed that all 11 carbon steel liners 

that had contained spent fuel showed much more evidence of external corrosion near the 

top of the fueled section than those containing electrical simulators (Weiss et al. 1985). The 

effect of gamma radiolysis on stress corrosion cracking has been described by Andresen 

88 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
(1992), who writes, “While IASCC (irradiation-assisted stress-corrosion cracking) is of 

primary interest in light water reactor core materials, it is also of concern in applications 

such as fusion reactors and high-level radioactive waste containers.” At this time, there is no 

discussion of the effect of chloride on IASCC in Yucca Mountain program documents. 

The fact that organic matter and nitrate can and do react, resulting in the loss of nitrate, may 

not be the end of nitrate (Peterman 2008). Oxides of nitrogen and nitric acid (secondary 

components) are produced by gamma radiolysis in moist air in the immediate vicinity of a 

waste package, as described by Tang and Raduescu. So, the situation exists now where nitrate 

may be produced and sorbed onto a waste package surface in a postclosure environment 

after the organic matter has been consumed by this continuous nitrate source. A material 

balance taking into account the kinetics of organic loss and nitrate production has not 

been completed. If this situation is subsequently shown to be the result, the corrosion 

environment will be nitrate-rich. It is clear at this time, though, that all the effects described 

here evolve with respect to time, and there is no material-balance description available that 

takes all these effects into account. 

The conceptual description of the corrosion environment of a waste package determined 

in part by atmospheric dust clearly has evolved in comparison to the description of 10 

years ago. The experience gained in this evolution applies to a description of any corrosion 

environment that results from exposure to the atmosphere and especially that expected 

for the long-term dry storage of spent nuclear fuel on the Earth’s surface, where naturalconvection cooling using the atmosphere will be implemented. We believe that most, if 

not all, future repositories will have extended preclosure periods. That is, the duration of 

the time between emplacement of a waste package and closure of the repository may be 

measured in decades. Dust will be deposited on waste packages surfaces during that period, 

and the composition of the dust will be affected by the five major factors discussed in this 

appendix. The composition of the dust determines the corrosion environment during the 

preclosure period and influences the corrosion environment during the period that begins 

immediately after closure. Thus, studying the evolution of the surface environment of the 

waste packages is important for any future repository. 

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Frizon, F, S Gin, C Jegou, “Mass Transfer Phenomena in Nuclear Waste Packages,” in (L.Q. 

Wang Ed.): Advances in Transport Phenomena, pp. 31-133, Springer-Verlag, 2009 

Garrick, BJ, Nuclear Waste Technical Review Board letter to the United States Department of 

Energy, July 2007 

Gelencsér, A, Carbonaceous Aerosol, Springer, The Netherlands, 2004 

Peterman, Z, “United States Geologic Survey: Effects of Temperature on the Composition of 

Soluble Salts in Dust,” presentation to the Nuclear Waste Technical Review Board, slide 

32, January 2008 

Prather, KA, Department of Chemistry, University of California at San Diego, e-mail to B 

Kirstein, April 8, 2010 

Sullivan, RC, SA Guazzotti, DA Sodeman, Y Tang, GR Carmichael, and KA Prather, “Mineral 

dust is a sink for chlorine in the marine boundary layer,” Atmospheric Environment, 41 p. 

7166-7179, 2007 

Tang, JS and G Raduescu, “Radiolytic Production of Nitric Acid Outside a 21-PWR Waste 

Package,” Radiation Protection & Shielding Division of the American Nuclear Society 

Biennial RPSD Topical Meeting, Proceedings of 12th Meeting, Santa Fe, NM, p. 818-821, 

April 14-18, 2002 

Weiss, H, RA Van Konynenburg, and RD McCright, Metallurgical Analysis of a 304L Stainless 

Steel Canister from the Spent Fuel Test – Climax, UCID-20436, Lawrence Livermore 

National Laboratory, 1985 

90 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
APPENDix A-2
 

iTErATivE NATUrE Of GEOLOGiC SiTE iNvESTiGATiON AND 

ChArACTEriZATiON 

In 1994, the Board held a meeting to review the successes and failures of various attempts 

to site and license large engineering projects, such as nuclear waste repositories, power 

plants, and dams (NWTRB 1994). On the basis of the meeting and subsequent analysis, 

the Board offered several insights and lessons learned that it believed would apply to the 

Yucca Mountain site characterization. Two related directly to geology: (1) Site assessment 

requires a strategy that is an iterative process that continually looks at the relationships 

among data gathering, modeling, and performance assessment; and (2) Expect surprises in 

any underground site investigation. Geologic surprises certainly appeared over the years of 

investigation at Yucca Mountain and affected the evolving conceptual model of site geology 

and repository design. DOE and the Yucca Mountain program remained sufficiently flexible 

to incorporate the surprises into project knowledge and modeling, but surprises sometimes 

led to project delays. 

Formal site-characterization work began at Yucca Mountain in 1977. Using surface 

geological mapping supplemented by preliminary borehole data, DOE constructed a 

preliminary subsurface conceptual model of site geology, which looked like Figure 1 (next 

page) in 1988. Figure 1 was based on data from more than 180 boreholes and 20 excavated 

trenches. The repository was expected to be located in the lower nonlithophysal zone, 

toward the bottom of the Topopah Spring rock unit (DOE 1988b: 1-326). Considerable 

additional site investigation was planned. Knowledge of all important geological rock 

units and features (for example, earthquake faults and rock fractures) was needed not 

only to design and construct the underground tunnels and rooms but also to predict the 

mechanical, thermal, hydrological, and geochemical behavior of the natural system far into 

the future. 

Since its first meetings in 1989, the Board emphasized the importance of gaining direct 

access to the underground at Yucca Mountain by excavating tunnels or drifts across all 

major geologic features at the site. As of 1993, DOE had prepared detailed site-investigation 

plans for tunneling through the mountain at various levels and across all geologic units to 

allow visual examination of the complex geology and to characterize the major geologic 

Appendix A-2 91 
Figure 1. East-west geologic model of Yucca Mountain in 1988 (DOE 1988a: 19) 

features in the planned repository block. The plans included extensive tunneling into Yucca 

Mountain: 8 tunnels and 88 rooms or “alcoves” for conducting in situ scientific tests. An 

unexpected 40 percent budget cut for the program in 1994-95 led to a significant reduction 

of tunneling plans. The first exploratory tunnel, the ESF, was started in September 1994 by a 

tunnel-boring machine and completed in April 1997 for a total distance of almost 5 miles. 

The ESF confirmed the basic model of rock strata, but the rock mass’s structural quality and 

expected number and nature of structural features (faults, major fractures, joint planes, and 

lithophysae) proved quite different from what was expected. Testing in the ESF also revealed 

the possibility of fast flow paths from the surface and long-term average flows that were 10 

times faster than previously thought. The new information resulted in many changes to the 

project assumptions. 

The ESF tunnel did not extend down deep enough to expose the rock where most 

of the repository was planned to be built. When DOE became reluctant to carry out 

additional tunneling because of budget cuts and schedule pressure, the Board stated, 

“It is the Board’s position that a technically defensible evaluation of the site cannot be 

made without exploration that would eliminate or greatly decrease the potential for a 

major geologic surprise subsequent to the decision. The Board continues to believe that 

an east-west crossing of the geologic block west of the Ghost Dance Fault (i.e., the upper 

92 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
waste emplacement block) is necessary prior to any technically defensible decision on site 

suitability.” (NWTRB 1996: 23) 

In early 1997, the Board repeated its position and added, “The Board believes that 

determining the existence and abundance of fast flow paths can best be accomplished by 

excavating an east-west tunnel through the potential repository block west of the existing 

ESF (NWTRB 1997: 8).” DOE accepted the Board’s recommendation for building the ECRB, 

a small-diameter east-west exploratory tunnel to be driven across the proposed repository 

block, and began excavating the ECRB by tunnel-boring machine in December 1997. The 

work was completed in October 1998, extending 1.6 miles from the ESF start point (the 

right side of Figure 2). The ECRB permitted observation of rock conditions at a different 

orientation than in the ESF, involved tunneling through the full range of repository rock 

units, and provided access to mine test rooms for scientific testing in new areas. 

Figure 2. Enhanced Characterization of the Repository Block (Cross Drift) 

New scientific insights were gained with information from the ECRB that affected the 

Yucca Mountain program. Fast-flow pathways of water were confirmed. Geologists formally 

identified the four key lithostratigraphic rock units (Tptpul, Tptpmn, Tptpll, Tptpln) in 

the proposed repository horizon on the basis of rock features (primarily lithophysae and 

fractures). Visual inspection of these units led to adoption of a more detailed geologic model 

in comparison to the model consisting of two thermo-mechanical geologic rock units (TSw1 

and TSw2) previously used. By 2002, DOE had relocated the repository from the Tptpln 

rock unit (planned location in 1988) to mostly (~80 percent) within the Tptpll rock unit. The 

Appendix A-2 93 
Tptpul upper lithophysal and Tptpll lower lithophysal units were significantly different from 

the Tptpmn and Tptpln nonlithophysal units, having different mechanical, thermal, and 

hydrological properties. Most of the hundreds of borehole specimens that were tested turned 

out to be biased because lithophysae were not well represented in the 1- and 2-in.-diameter 

borehole core specimens. The ECRB and its test alcoves also revealed important information 

about in situ rock moisture, major fault features, failed lithophysae or “spot” features, data 

needed to improve the three-dimensional geologic rock model, and various rock properties. 

Yucca Mountain geology has not changed over the years of investigation; only human 

knowledge about the geology has changed. Inevitably, any investigation of future repositories 

will encounter its share of surprises, and the understanding of the geology will evolve, 

particularly after underground access is provided. 

rEfErENCES 

BSC (Bechtel SAIC Company), Subsurface Geotechnical Parameters Report, ANLSSD-GE-000001 REV 00, January 2007, Las Vegas, NV. Figure 6-4, p. 6-16. Figure is 

based on one given in a 1999 U.S. Geological Survey report. 

DOE (U.S. Department of Energy), Environmental Assessment, Yucca Mountain Site, Nevada 

Research and Development Area, DOE/RW-0073, 1986, Washington, D.C. 

DOE (U.S. Department of Energy), Site Characterization Plan: Overview, December 1988a, 

portion of Figure 2-3, p. 19 

DOE (U.S. Department of Energy), Site Characterization Plan, December 1988b, Volume 1, 

Part A, p. 1-326 

DOE (U.S. Department of Energy), “The U.S. Department of Energy Moves Forward with the 

Release of Final Performance Requirements for Canister System,” Washington, D.C., June 

19, 2007 

DOE (U.S. Department of Energy), Yucca Mountain Repository License Application for 

Construction Authorization, (17 Volumes), June 3, 2008 

NWTRB (Nuclear Waste Technical Review Board), 1994 Findings and Recommendations, Report 

to the U.S. Congress and the U.S. Secretary of Energy, Arlington, Virginia, March 1995 

NWTRB (Nuclear Waste Technical Review Board), 1995 Findings and Recommendations, 

Report to the U.S. Congress and the U.S. Secretary of Energy, Arlington, Virginia, April 1996 

NWTRB (Nuclear Waste Technical Review Board), January to December 1996, Report to the 

U.S. Congress and the U.S. Secretary of Energy, Arlington, Virginia, March 1997 

94 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
APPENDix A-3
 

ThErMAL MANAGEMENT 

The Board expressed interest in DOE’s Yucca Mountain repository thermal management 

strategy that resulted in the repository design layout, designation of a single thermal loading, 

and preclosure operations based on this single thermal loading that appear in DOE’s license 

application. The repository design characteristics, which are a direct result of DOE’s thermal 

strategy, are a drift spacing of 81 meters, an axial waste package spacing of 0.1 meter, 

designation of a single thermal line load at emplacement of 1.45 kilowatts/meter with a 

specific rate of decay, and preclosure forced-air ventilation (CRWMS M&O 1999). 

Over many years, the Board questioned the thermal management strategy. DOE’s thermal 

management strategy did evolve because of, in part, more time-efficient thermal analysis 

techniques, but the evolution did not include varying thermal loads for use in the Total 

System Performance Assessment (SNL 2008). The more time-efficient thermal analysis 

techniques that came into existence include the ventilation calculation, where decay heat 

from emplaced waste packages is removed by forced ventilation of ambient air through 

the repository to remove a significant fraction of the heat. This ventilation analysis initially 

required so much time that various thermal strategies simply could not be analyzed 

thoroughly. However, as time passed, thermal analysis techniques were improved to the 

point where many thermal analyses could be completed in much less time. 

The improved ventilation analysis resulted in computational times of seconds compared 

with many hours previously (Walsh 2004). The purpose of the ventilation analysis was to 

calculate how much heat from waste packages would be transferred to the host rock and 

how much would leave the repository in the ventilation air flow. The result of the ventilation 

analysis was a fraction, called the “ventilation efficiency,” that denotes how much heat leaves 

in the flowing air relative to that produced in the waste packages. 

DOE’s approach originally was based on numerically integrating the classical transient 

heat-transfer equation for a solid for the entire mountain at every time step—a conceptually 

correct approach but one that required computational times on the order of many hours. 

The improved ventilation analysis is based on the fact that the classical heat-transfer 

equation for a solid is linear and that a description of rock temperature can be derived from 

Appendix A-3 95 
the temperature response of the rock that is due to a single short pulse input of energy. The 

temperature of the rock can be computed for any transient heat source from the single-pulse 

response, and the single-pulse response is calculated only once analytically and used over 

and over to move the analysis forward in time. This technique, known as “superposition,” 

eliminated the numerical integration step. The same mathematical approach applies to 

the postclosure situation, where there is very little air flow. The improved computational 

approach enabled analyses of a loss-of-forced-ventilation condition, where the flow occurred 

only because of buoyancy, also called “natural convection,” of heated air in the vertical 

ventilation shafts. The ability to perform thermal analyses on the order of seconds allowed 

the investigation of many thermal strategies; this could not be done previously. 

The Board undertook thermal analysis efforts so that it would be in a position to understand 

better the various thermal issues and to direct questions to DOE from a position of informed 

inquiry. As in DOE’s thermal analysis, the Board based its thermal analysis efforts on 

classical heat-transfer theory and models. However, the Board used different mathematicalsolution techniques from the literature. To ensure that the Board’s calculations were correct, 

the Board compared its results with those of DOE and found close agreement. The Board’s 

efforts showed that any waste package that could be shipped from a power plant to the 

repository could be emplaced in the repository immediately on receipt without exceeding 

any repository thermal criterion (Rowe and Kirstein 2008). This result essentially eliminated 

the need for temporary storage at the repository. In contrast, the emplacement pattern 

called for in the license application required either that the thermal power of shipped waste 

packages be closely controlled or that waste packages be accumulated in storage at the 

repository until they decayed to an appropriate thermal power level for emplacement. 

DOE also completed thermal analyses for a range of anticipated repository thermal 

loadings and concluded that through additional thermal management strategies, such as 

increased spacing between hotter packages and longer preclosure ventilation periods, the 

anticipated thermal-power range of packages that could be shipped could be accommodated 

satisfactorily (i.e., immediately emplaced) in the repository (Hardin 2008). 

The effective thermal conductivity of crushed rock (e.g., backfill and rockfall granular 

material) is needed for thermal analyses. DOE’s M&O contractor estimated that the nominal 

diameter of backfill and rockfall granular material in a Yucca Mountain repository would 

be 10 centimeters (BSC 2004). Classical methods for estimating the effective thermal 

conductivity of crushed rock from intact rock properties do not apply, because they 

assume that the nominal diameter of the granular material is on the order of that of sand. 

In contrast to the effective thermal conductivity of fine-grain material such as sand, the 

effective thermal conductivity of coarse-grain material is strongly influenced by radiantheat transfer through the voids between the particles (Buscheck 2005). In fact, the effective 

96 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
thermal conductivity of coarse crushed tuff is two to three times greater than the thermal 

conductivity of fine crushed tuff. This has been experimentally verified (Osnes et al. 2008). 

Thus, the thermal effects of backfill and rockfall granular material around a heat-producing 

waste package now can be analyzed for any repository with greater accuracy and confidence. 

The improved method for estimating thermal conductivity of granular material and moreefficient computational techniques are applicable to future repository analyses and will yield 

improved prediction of the thermal environment. 

rEfErENCES 

BSC (Bechtel SAIC Company), Drift Degradation Analysis, ANL-EBS-MD-000027, Rev 03, 

Section 6.4.2.5, 2004 

Buscheck, TA, Multiscale Thermohydrologic Model, ANL-EBS-MD-000049, Rev 03, Appendix 

XI, 2005 

CRWMS M&O (Civilian Radioactive Waste Management System Management and 

Operating Contractor), License Application Design Selection Report, B00000000-01717­

4600-00123, Rev 01, ICN 01, Las Vegas, Nevada, ACC: MOL.19990908.0319, and related 

documents, 1999 

Hardin, EL, Postclosure Analysis of the Range of Design Thermal Loadings, ANLNBS-HS-000057, Rev 00, Bechtel SAIC Company, LLC, 2008 

Osnes, JD, RL Jones, and KD Mellegard, Experiment to Determine the Effective Thermal 

Conductivity of Coarse, Dry Backfill, LLR.20081023.0023, 33 pages, August 28, 2008 

Rowe, GW and BE Kirstein, Thermal-Response Evaluation of Yucca Mountain During the 

Preclosure and Postclosure Phases, Nuclear Waste Technical Review Board, 27 pages plus 

appendices, 2008 

SNL (Sandia National Laboratories), Total System Performance Assessment Model/Analysis for 

the License Application, ANL-WIS-MD-000005 REV 00, page ES-40, Figure ES-42, 

January, 2008 

Walsh, R, Ventilation Model and Analysis Report, ANL-EBS-MD-000030, Rev 04, Bechtel 

SAIC Company, LLC, 2004 

Appendix A-3 97 

APPENDix A-4
 

SUMMArY Of ThE OCTOBEr 2010 U.S. NUCLEAr WASTE TEChNiCAL 

rEviEW BOArD MEETiNG ON LESSONS LEArNED frOM hiGhACTiviTY WASTE MANAGEMENT AND DiSPOSAL EffOrTS iN ThE 

UNiTED STATES AND OThEr COUNTriES 

On October 26, 2010, the U.S. Nuclear Waste Technical Review Board held a public meeting 

in Dulles, Virginia. The theme of the meeting was “Technical Experience Gained During 

Development of the Yucca Mountain Repository Program.” The purpose of the meeting was 

to elicit technical lessons that would be of value to future U.S. efforts in waste management 

and disposal. The Board invited interested parties having involvement in or knowledge 

of the Yucca Mountain repository program to provide their views of lessons that could be 

learned from the U.S. program from their individual perspectives. 

The meeting was organized into three panels: Panel I, which was composed of former 

Yucca Mountain managers, scientists and engineers, and contractors; Panel II, which was 

composed of representatives of affected state and local governments; and Panel III, which 

was composed of representatives of key programs in other countries. 

Some selected highlights from the discussions are presented below. Transcripts from the 

meeting and the full presentations of meeting participants can be viewed on the Board’s Web 

site at www.nwtrb.gov. 

PANEL i: viEW frOM WiThiN ThE YUCCA MOUNTAiN PrOjECT 

Yucca Mountain in Nevada was designated in the 1987 amendments to the Nuclear 

Waste Policy Act as the sole site to be characterized for its suitability as the location of 

permanent geologic repository for the disposal of high-activity nuclear waste. Following the 

designation, an extensive program was initiated to continue investigating the site, which had 

been under investigation as a potential repository site for 10 years, and to design a repository 

that would combine engineered and natural barriers for isolating radionuclides from the 

accessible environment for millennia. 

Appendix A-4 99 
This first-of-its-kind effort involved many activities in addition to characterizing the site and
 

designing the repository, including developing an estimate of the system performance of the
 

repository that would become part of a repository license application; designing a waste-


management system, including packaging and transporting the waste; and anticipating
 

and planning the design and operation of the repository surface facilities. Many talented
 

scientists and engineers were involved in this technical and scientific effort, and the Board
 

invited some of them to present and discuss their thoughts at the October 26, 2010, meeting.
 

The panel members were Dr. Russell Dyer, former Yucca Mountain Project Manager and
 

Chief Scientist; Mr. Tom Coleman, former Subsurface Engineering Manager for USA RS;
 

Mr. Ted Feigenbaum, former General Manager, Bechtel-SAIC Company, LLC; and
 

Dr. Jean Younker, former Deputy Assistant General Manager, Bechtel-SAIC Company, LLC.
 

The panel was asked to address the following questions:
 

1.	 What technical advances were made during development of the program that would be 

applicable in developing future programs for management of spent nuclear fuel (SNF) 

and high-level radioactive waste (HLW) in the United States? 

2.	 What scientific research or technical development work would be undertaken now 

or in the near term to support future development of a repository for disposal of 

SNF and HLW? 

3.	 How did different managerial approaches and changes in management approach during 

the development of the program influence the design, planned operations, and logistics 

of the Yucca Mountain program? 

Selected highlights from the panel presentations and discussion among the panelists and 

Board members are paraphrased below. 

•	 Integration of science and engineering is very important.

•	 Flexibility is a key asset in designing a high-activity-waste program and repository;

Total System Performance Assessment should be more user-friendly and flexible. 

•	 Focus on validation of models of an ambient, undisturbed site, and then use expert

judgment to deal with disruptive events; begin long-term testing on key processes early. 

•	 Frequent changes in budgets and program managers make managing the program

challenging; establish long-term capital budgets. 

•	 Use prime contractors who have experience with nuclear projects, and bring them

in early. 

100 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
•	 Designating a “lead-lab” increases efficiency and effectiveness.
 

•	 Prototyping of key engineered components can prevent their becoming critical-path

issues and can increase public confidence. 

•	 Design of transportation and storage canisters should be standardized; designs should

reflect different requirements and changing needs. 

•	 Direct disposal of dual-purpose canisters should be considered.

•	 Predicting the performance of materials used for engineered barriers is not difficult

if the repository environment is known, but knowing the repository environment is 

challenging; model results can be very assumption-dependent. 

•	 Decisions should be made on the bases of science, economics, and public safety, not on

politics. 

•	 The Yucca Mountain experience would facilitate the characterization of another site in

this country because the implementers now know better what kind of questions to ask. 

•	 In terms of site criteria, disruptive events for any site chosen will be key, and climate

change will have to be bounded. 

•	 Uncertainty is introduced by changing the standard late in the license preparation

process. 

•	 The project took a conservative approach in terms of the overall objective, which was

to get Yucca Mountain licensed. Some believe that the conservatisms were excessive 

or unnecessary. 

•	 Future repository programs should be able to use the existing system model and finetune it for the specific site. 

•	 Lack of state and community support helped determine the fate of the Yucca Mountain

repository program. 

PANEL ii: viEWS Of AffECTED STATE AND LOCAL GOvErNMENTS 

The Nuclear Waste Policy Act directs the Secretary of Energy to make grants to the State of 

Nevada and units of local governments in the geographical area that would be affected by 

the Yucca Mountain repository. The purpose of the funding is to enable the state or affected 

units to develop a request for impact assistance; engage in monitoring, testing, or evaluating 

activities related to site characterization; and provide and request information. The affected 

governments included the State of Nevada; Nye County (in which Yucca Mountain is 

located); Clark County (which adjoins Nye County and in which Las Vegas is located); and 

Appendix A-4 101 
other counties abutting Nye County, including Inyo County, California, and the Nevada 

counties of Lincoln, White Pine, Eureka, Lander, Churchill, Mineral, and Esmeralda. 

Some of the affected governments have used a portion of the funding for technical studies 

that were performed independent of the Department of Energy (DOE). Examples of the 

subjects of such studies include the following: 

•	 Evolution of environments on waste-package surfaces (Nye County)

•	 Hydrology of the saturated zone in a southwest direction from Yucca Mountain (Nye

County and Inyo County) 

•	 Ventilation methods for heat removal from a repository in Yucca Mountain (Nye

County) 

•	 Socioeconomic studies and social perceptions of impacts of Yucca Mountain (Clark

County) 

•	 Impacts of Yucca Mountain on national and in-Nevada transportation of SNF and

HLW (State of Nevada) 

Since its inception, the Board has interacted with representatives of the affected governments 

and has heard presentations on these studies. The Board invited a panel of representatives of 

affected governments to present their views on their experiences. 

Panel members were Mr. Steve Frishman, Technical Consultant to the State of Nevada; 

Ms. Abigail Johnson, Nuclear Waste Advisor, Eureka County, Nevada; Ms. Irene Navis, 

Director of Emergency Management and Homeland Security, Clark County, Nevada; 

Ms. Connie Simkins, Coordinator of Nuclear Oversight Program, Lincoln County, Nevada; 

and Mr. Joe Ziegler, Consultant on Nuclear Safety and Licensing, Nye County, Nevada. 

The Panel was asked to address the following questions: 

1.	 How has oversight performed by affected units of governments influenced technical 

decisions related to nuclear waste management and disposal? 

2.	 What factors increased the effectiveness of the technical oversight? What factors might 

have reduced the effectiveness of such oversight? 

3.	 How does the performance of technical oversight affect the confidence of units of local 

government and the public in the validity of the technical process? 

102 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
Selected highlights from the panel presentations and discussion are paraphrased below. 

•	 The perception is that local and state oversight or participation was resisted by the

implementer (U.S. Department of Energy) and that comments by affected governments 

were ignored. 

•	 Oversight should not be categorized as “technical” or “nontechnical” because many

of the greatest challenges are institutional; e.g., economic, management, policy, and 

systems. 

•	 The concept of oversight needs an overhaul, both from the standpoint of the mindset of

the implementers and the mechanics of the process. 

•	 State and local governments were not invited to be part of the NEPA process, which

reduced confidence in the process. 

•	 The technical process must be valid for affected parties to have confidence in it.

•	 Communicating technical information so that it is understandable to the lay public is

key to increasing confidence. 

•	 Funding of local and state government oversight needs to be adequate and consistent

so that affected governments can conduct independent research, monitoring, and 

reporting. 

•	 In the opinion of some affected governments, the benefits of the repository project

were not adequately presented to the public. 

•	 Board meetings provided opportunities for affected governments and the public to

interact with the implementers; the charter of the Board should be broadened. 

•	 There should be a federal commitment to local and state oversight, established by law.

•	 Early access to and transparency of program data are crucial for public confidence

•	 The U.S. Nuclear Regulatory Commission’s relationship with the applicant should be

transparent and at arm’s length. 

•	 Sufficient time needs to be provided for the public to respond to proposed rule changes

and federal decisions. 

•	 If the host state opposes the proposed repository site, nothing will satisfy objections

until the project is terminated. 

•	 If affected governments see their comments reflected in decision-making, confidence

increases. If they do not see any result from their oversight, confidence is decreased. 

Appendix A-4 103 
PANEL iii: viEW frOM OThEr COUNTriES 

The very-long-term management and ultimate disposition of high-activity waste from
 

commercial nuclear power generation and from defense activities is an increasingly high
 

priority for many countries. Over time, a strong international consensus has emerged that
 

deep geologic disposal is feasible and that it is the preferred mode of disposing of such waste.
 

A broad range of approaches toward developing and siting deep geologic repositories is
 

being pursued by national programs. Each approach takes into consideration the operational
 

needs, geology, and socioeconomic circumstances that are specific to the country in which
 

the repository would be located. The approaches taken by the counties have similarities and
 

differences, and the pace of the programs differ.
 

Over the years, the Board has interacted with its counterparts in other countries as well
 

as with the implementers of numerous waste-management programs. These international
 

exchanges have been extremely valuable in the Board’s ongoing review of DOE repository
 

development efforts in the United States. As part of the Board’s discussion of lessons that can
 

be learned from repository development efforts to date, the Board invited representatives of
 

waste-management programs of four countries to provide information on the status of their
 

programs and their views of the Yucca Mountain program.
 

The panel members were Dr. Enrique Biurrun, Head of the International Cooperation 


Department, DBE TECHNOLOGY GmbH, Germany; Mr. John Mathieson, Head of 


International Relations, Nuclear Decommissioning Authority, United Kingdom; 


Dr. Gérald Ouzounian, Director at the Head of the International Division, Andra 


(National Agency for Radioactive Waste Management, France; and Dr. Olof Söderberg, 


Consultant to SKB (Swedish Nuclear Fuel and Waste Management Company), Sweden. 


The panelists were asked to respond to the following questions:
 

1.	 As you were observing the Yucca Mountain program, what technical approaches 

seemed to be the most persuasive in terms of making a safety case? Which were the least 

persuasive? Which seemed to be at odds with the prevailing international consensus? 

2.	 If a new effort for waste management and disposal were to be launched in the United 

States, what would be the three most important lessons your country has learned that 

should be taken into account? 

3.	 Which aspects of the Yucca Mountain program and the repository program in your 

country indicated technical features or developments that should be avoided in 

developing a repository program in the United States? 

104 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
 Selected highlights from the panel presentations and discussion are paraphrased below. 

•	 When a project (repository) is stopped, it is difficult to move ahead in the future.

•	 Developing and demonstrating waste isolation in the repository host rock before the

repository is licensed is a real advantage. 

•	 A simple component of the waste-management system can be the one that causes the

most problems. 

•	 It is helpful to have responsibilities and the steps of repository development established

by law (as in the Nuclear Waste Policy Act). 

•	 Financing of repository efforts by waste producers who reimburse expenditures on the

basis of multiyear plans has many advantages over the U.S. system of funding disposal 

activities from the dedicated Nuclear Waste Fund. 

•	 Changes in the U.S. waste isolation concepts (e.g., cool to hot, wet to dry, geologic to

engineered) are hard for programs outside the United States to understand. 

•	 Some programs’ safety concepts rely on maintaining the integrity of the geologic

barrier rather than on meeting a health safety standard for a specified period (as in the 

United States). 

•	 Countries that recycle have many different kinds of nuclear waste.

•	 Adopting an approach of “decide, announce, defend” can foment strong local opposition.

•	 Extensive consultation with the public is important.

•	 The “government,” not the implementer, should lead the effort to find a repository site.

•	 When efforts to site a repository fail, maintaining a core of competent scientists

and engineers with experience in the program and retaining data and information 

produced by the program are important. 

•	 Involvement and advice by social scientists is important in effective engagement with

the public. 

•	 When offering benefits for hosting a site, it is very important that the process be transparent

and aboveboard to prevent any appearance of trying to “bribe” the community. 

•	 Until the point that the repository is in the construction phase, it is important that the

host community have a veto over the development of a repository. 

•	 Work at the stakeholders’ speed.

Appendix A-4 105
•	 Reversability (retrievability) is necessary for public confidence.

•	 The public may be willing to take the recommendations of scientists related to the

underground facilities, but they want a say in the location of the surface facilities. 

•	 The following set Sweden’s program apart from the U.S. program: physical magnitude

of the waste problem; Sweden’s absence of military waste; the differences in 

governmental systems; program implementer is a governmental entity in the United 

States, but in Sweden it is a private corporation owned by nuclear power plants. 

•	 In Sweden and other countries, oversight boards have a purview that includes ethical,

legal, social, and policy dimensions of waste management. This is a broader purview 

than that of the NWTRB. 

•	 Decision on going forward should not be postponed into an uncertain future.

•	 Openness and willingness to discuss difficult issues have been key to the success of

the repository program in Sweden. Providing local governments their own money for 

participating in the process also was key. 

•	 Britain does not have laws governing their repository siting process, so it is done

through consultation. 

•	 After failure of a program, several countries have found that it takes approximately 10

years to restart the effort. 

•	 In some countries, opposition to a repository is a way to oppose nuclear activities

in general. 

•	 The safety case in some countries is based on a zero release; safety criteria are expressed

in dose because the dose is understood better by the public. 

•	 In the UK, safety criteria become more qualitative as the regulatory period gets longer.

PUBLiC COMMENT 

The Board provides opportunities for public comment at its meetings. Following are 

highlights from public comments at the October 26, 2010, meeting. 

•	 Get a national agreement that a repository is needed; describe the problem and how

the repository solves it; deal with existing waste. 

•	 Replacing the existing waste with new waste is a whole different conversation.

106 Technical Advancements and Issues Associated with the Permanent Disposal of High-Activity Wastes 
•	 A standard needs to be set, and zero release is a reasonable expectation for people

living next to the repository. 

•	 Incentives should be provided for people who are willing to accept a repository.

•	 A volunteer or a willing host will be necessary for the repository to succeed.

•	 In other countries, repository sites are located near other nuclear facilities.

Appendix A-4 107 


United States

Nuclear Waste Technical Review Board

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Suite 1300

Arlington, VA 22201

(703) 235-4473

www.nwtrb.gov