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Technical B- To ve a.. Mountain ~ - ..~ - .~o Committee on Technical Bases for Yucca Mountain Standards Board on Raclioactive Waste Management Commission on Geosciences, Environment, anc! Resources National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1 995

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NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn Tom the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. Support for this study on Technical Bases for Yucca Mountain Standards was provicie(i by the U.S. Environmental Protection Agency, uncler contract number 68D30014. Library of Congress Catalog Card No. 95-69192 International Standard Book Number 0-309-05289-0 Additional copies of this report are available from: National Academy Press 2 1 0 1 Constitution Avenue' N. W. Box 285 Washington, D.C. 20055 Call 800-624-6242 or 202-334-3313 (in the Washington Metropolitan Area). B563 Copyright 1995 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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COMMITTEE ON TECHNICAL BASES FOR YUCCA MOUNTAIN STANDARDS ROBERT W. FRI, Chair, Resources for the Future, Washington, DC, JOHN F. AHEARNE, Sigma Xi, The Scientific Research Society, Research Triangle Park, North Carolina JEAN M. BAHR, University of Wisconsin, Madison R. DARRYL BANKS, World Resources Institute, Washington, DC ROBERT J. BUDNITZ, Future Resources Associates, Berkeley, California SOL BURSTEIN, Wisconsin Electric Power, Milwaukee (retired) MELVIN W. CARTER, Georgia Institute of Technology, Atlanta (professor emeritus) CHARLES FAIRHURST, University of Minnesota, Minneapolis CHARLES McCOMBIE, National Cooperative for the Disposal of Radioactive Waste,Wettingen, Switzerland FRED M. PHILLIPS, New Mexico Institute of Mining and Technology, Socorro THOMAS H. PIGFORD, University of California, Berkeley, Oakland (professor emeritus) ARTHUR C. UPTON, New Mexico School of Medicine, Santa Fe CHRIS G. WHIPPLE, ICE Kaiser Engineers, Oakland, California GILBERT F. WHITE, University of Colorado, Boulder SUSAN D. WILTSHIRE, JK Research Associates, Inc., Beverly, Massachusetts Staff MYRON F. UMAN, Study Director RAYMOND A. WASSEL, Senior Staff Officer ROBERT J. CROSSGROVE, Copy Editor LISA J. CLENDEN1NG, Senior Project Assistant . . .

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BOARD ON RADIOACTIVE WASTE MANAGEMENT MICHAEL C. KAVANAUGH, Chair, ENVIRON Corporation, Emeryville, California B. JOHN GARRICK, Vice-Chair, PLG, Incorporated, Newport Beach, California JOHN F. AHEARNE, Sigma Xi, The Scientific Research Society, Research Triangle Park, North Carolina JEAN M. BAHR, University of Wisconsin, Madison LYNDA L. BROTHERS, Davis Wright Tremaine, Seattle, Washington SOL BURSTEIN, Wisconsin Electric Power, Milwaukee (retired) MELVIN W. CARTER, Georgia Institute of Technology, Atlanta (professor emeritus) PAUL P. CRAIG, University of California, Davis (professor emeritus) MARY R. ENGLISH, University of Tennessee, Knoxville ROBERT D. HATCHER, JR., University of Tennessee/Oak Ridge National Laboratory, Knoxville DARLEANE C. HOFFMAN, Lawrence Berkeley Laboratory, Berkeley, California H. ROBERT MEYER, Keystone Scientific, Inc., Fort Collins, Colorado PERRY L. McCARTY, Stanford University, California CHARLES McCOMBIE, National Cooperative for the Disposal of Radioactive Waste, Wettingen, Switzerland PRISCILLA P. NELSON, Universtiy of Texas at Austin D. KIRK NORDSTROM, U.S. Geological Survey, Boulder, Colorado D. WARNER NORTH, Decision Focus, Incorporated, Mountain View, California GLENN PAULSON, Illinois Institute of Technology, Chicago PAUL SLOVIC, Decision Research, Eugene, Oregon BENJAMIN L. SMITH, Independent Consultant, Columbia, Tennessee Staff CARL A. ANDERSON, Staff Director KEVIN D. CROWLEY, Associate Director ROBERT S. ANDREWS, Senior Staff Officer K~ARYANIL T. THOMAS, Senior Staff Officer SUSAN B. MOCKLER, Research Associate THOMAS KIESS, Staff Officer ROBIN L. ALLEN, Senior Project Assistant REBECCA BURKA, Senior Project Assistant LISA J. CLENDENING, Senior Project Assistant DENNIS L. DUPREE, Senior Project Assistant SCOTT A. HASSEL, Project Assistant PATRICIA A. JONES, Project Assistant IV

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COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES M. GORDON WOLMAN, Chair, The Johns Hopkins University, Baltimore, Maryland PATRICK R. ATKINS, Aluminum Company of America, Pittsburgh, Pennsylvania EDITH BROWN WEISS, Georgetown University Law Center, Washington, DC JAMES P. BRUCE, Canadian Climate Program Board, Ottawa WILLIAM L. FISHER, University of Texas, Austin EDWARD A. FRIEMAN, Scripps Institution of Oceanography, La Jolia, California GEORGE M. HORNBERGER, University of Virginia, Charlottesville W. BARCLAY KAMB, California Institute of Technology, Pasadena PERRY L. McCARTY, Stanford University, California S. GEORGE PHILANDER, Princeton University, New Jersey RAYMOND A. PRICE, Queen's University at Kingston, Ontario, Canada THOMAS C. SCHELLING, University of Maryland, College Park ELLEN SILBERGELD, University of Maryland Medical School, Baltimore, Maryland STEVEN M. STANLEY, The Johns Hopkins University, Baltimore, Maryland VICTORIA J. TSCHINKEL, Landers and Parsons, Tallahassee, Florida Stay STEPHEN RATTIEN, Executive Director STEPHEN D. PARKER, Associate Executive Director MORGAN GOPNIK, Assistant Executive Director JAMES E. MALLORY, Administrative Officer SANDRA S. FITZPATRICK, Administrative Associate v

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The National Academy of Sciences is a private, nonprofit, self- perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and In the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Harold Liebowitz is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. Harold Liebowitz are chairman and vice chairman, respectively, of the National Research Council. Vl

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PREFACE In Section 801 of the Energy Policy Act of 1992 (P.L. 102-486), the U.S. Congress directed the U.S. Environmental Protection Agency (EPA) to promulgate standards to ensure protection of public health from high-level radioactive wastes in a deep geologic repository that might be built under Yucca Mountain in Nevada. By this provision, EPA must set the standards to ensure protection of the health of individual members of the public. The standards will apply only to the Yucca Mountain site. To assist EPA in this endeavor, Congress also asked the National Academy of Sciences to advise the agency on the technical bases for such standards. This report contains that advice. It was prepared by a committee organized under the auspices of the National Research Council, which is jointly managed by the National Academy of Sciences and the National Academy of Engineering for the purpose of conducting studies such as this. Biographical information on the members of our committee is presented in Appendix A. Our charge was contained explicitly in Section 801(a)~2) of the Act and elaborated in the Conference Report accompanying the bill as well as in correspondence from the Chairman of the Senate Committee on Energy and Natural Resources, Senator J. Bennett Johnston. These documents are contained in Appendix B. The charge consisted oftwo parts. The first was to address three specific questions contained in Section 801 Am. The second was to advise EPA on the technical basis for the health-based standards that it is mandated to prepare. To accomplish both objectives of the charge, we structured our study to focus on the state of scientific and technical understanding available for assessing the future behavior of an underground repository and for devising appropriate standards. We also took account of the eventual need for the U.S. Department of Energy (DOE) to demonstrate compliance with the standarcis. In the process, we conducted a series of five open technical meetings to assure that we had access to all of the analyses, including those in the international literature, that might pertain to our task. We invited to these meetings more than 50 nationally and internationally known scientists and engineers in pertinent fields to discuss the technical issues with us. At the final open meeting, we received recommendations from a number of observers about what they hoped would be in our report. . . V11

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. . . V111 YUCCA MOUNTAINSTANDARDS The information provided by invited experts and public participants has been most valuable to our work. The three Federal agencies involved (the U.S. Nuclear Regulatory Commission (USNRC), in addition to DOE and EPA), state and county agencies in Nevada, and private organizations, such as the Electric Power Research Institute all of which have sponsored research on the technical issues before us generously shared their data and insights with us. We also retained two consultants, Paul Dejonghe (Nuclear Energy Research Center, Mol. Belgium (retired)) summarizer! for us the experience of other countries in setting standards for high-level radioactive waste repositories, and DetIof von Winterfeldt (University of Southern California, Los Angeles) reviewed the literature on human intrusion into a repository at some time in the future and institutional controls to mitigate such intrusions. All of the information we received is available to the public. Although we believe that the full range of scientific information related to the standards was available to us, it became clear in the course of our work that designing the standards requires making decisions based as much or more on policy considerations than on science. It is equally clear that there is no sharp dividing line between science and policy. In developing this report, we have recognized that the committee members can speak as experts only on matters of science, but we have not construed our assignment so narrowly as to limit the usefulness of our recommendations for standard-setting in the real world. In short, we have commented on policy issues where we thought it necessary. Science alone cannot answer policy questions, however, and so we do not make policy recommendations in this report on the grounds that there is by definition a limited scientific basis for selecting one policy alternative over another. We have instead tried to use available technical information and judgment to suggest a starting point for the rulemaking process that will lead to a policy decision. By applying this approach consistently throughout the report, we have achieved consensus on a number of complex and controversial issues. In particular, we agree on the answers to the questions posed by Congress, the technical bases for health-based standards, and most of the elements of a procedure for assessing compliance with the standards. On one aspect of the compliance assessment procedure, however, one member of the committee has prepared a personal statement presented in Appendix E, outlining where his views diverge from the view of the rest of the committee. As chair of the committee, I have provided my perspective on that statement in Appendix F.

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PREFACE IX The issue in question concerns what assumptions to make about the future distribution of individuals that would be exposed to any possible releases from the repository. Assessing compliance, which would! be required in any licensing procedure, requires that the populations or individuals at risk be specified so their exposures or risks can be estimated and compared with the standards. Because the population at greatest risk from repository releases will exist far in the future, that population and its distribution are not amenable to scientific prediction. Developing a complete exposure scenario for compliance analysis therefore requires making assumptions about who will be at risk. While scientific information can be valuable in developing these assumptions, the choice of assumptions is ultimately a matter for policy judgment. In the committee's view, there are two avenues for approaching the construction of exposure scenarios. The two are summarized and compared in Chapter 3 and described in detail in Appendixes C and D, respectively. The committee offers these approaches as options for regulators to consider ~ . in specifying an exposure scenario. The personal statement by one committee member in Appendix E argues that only one of these approaches is appropriate. Although others may have an equally strong preference for the other approach, the remainder of the committee has preferred to follow its consistent practice of not taking a position on policy questions. On behalf of my colleagues on the committee, I wish to express our appreciation to all those who provided us with valuable input for our task. In particular, at our request, several agencies formally designated liaisons to the committee whose assignments were to assure that we were fully informed of the data and analyses that were available to their respective agencies. In turn, through the liaisons, we shared all of the information we obtained during the course of our work with their agencies. The liaisons were J. William Gunter, EPA; Margaret Federline, USNRC; Stephen J. Brocoum, DOE; Les W. Bradshaw, Nye County (Nevada) Nuclear Waste Repository Program; and Engelbrecht von Tiesenhausen, Clark County, Nevada. Robert Loux performed a similar function, although informally, for the State of Nevada Nuclear Waste Projects Office. Rosa Yang made sure that we were iffily informed of the results of research performed under the auspices of the Electric Power Research Institute. We are indebted to these individuals for their dedication to providing us with information. Finally, our work, while difficult enough, would have been even more so without the dedicated support ofthe NationalResearch Council

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Cam ~ Worsen Myron Um=, Lisa Clendening, Id oglers who ago Raised He committee. Bed W. hi Chad

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C O N T E N T S EXECUTIVE SUMMARY CHAPTER 1 - INTRODUCTION 15 SCOPE OF THE STUDY 18 BACKGROUND AND APPROACH .................... The Repository System ........................... Issues to Be Considered in Approaching the Study ...... Large but improbable doses .................. Demonstration of compliance ................. Fundamental sirs. derived standards ............. Time scale ................................ Choices Affecting the Bases of the Standard ........... CHAPTER 2 - PROTECTING HUMAN HEALTH .............. THE HEALTH EFFECTS OF IONIZING RADIATION DEVELOPMENT OF RADIATION PROTECTION STANDARDS .......................... . . .. .. . . - . 23 23 27 27 28 29 29 30 33 34 39 General Consensus in Radiation Protection Principles and Standards 39 THE FORES OF THE STANDARD 41 ELEMENTS OF AN INDIVIDUAL-RISK STANDARD 47 What Level of Protection? 49 Who Is Protected? 49 For HowI`on~? 54 57 58 59 PROTECTING THE GENERAL PUBLIC PROTECTING THE GLOBAL POPULATION NEGLIGIBLE INCREMENTAL RISK .............. PROTECTING LOCAL POPULATIONS . . . .. .. . . .. . . . . . . 61 Population-Risk Standard ......................... Spatial Gradient in Risk .......................... PREFERRED FORM OF THE STANDARD CHAPTER 3 - ASSESSING COMPLIANCE rNTRODUCTION . .... Xl 61 62 63 67 67

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. . X11 YUCCA MO UNTAIN STY NDAh1)S PART I: OVERVIEW OF PERFORMANCE ASSESSMENT 70 Reasonable Confidence 70 Time scale Probabilistic Analysis of Risk QUANTITATIVE CALCULATION OF REPOSITORY PERFORMANCE ............................... Elements of Performance Assessment ................ 71 72 73 74 Conceptual mode! 74 Mathematical mode} 76 76 Numerical analysis Mode! parameters 76 Bounciary conditions 77 Treatment of Uncertainty 7X Probabilistic modeling 78 Bounding estimates 79 Alternative conceptual models 79 80 Summary PATHWAYS AND PROCESSES FOR PERFORMANCE ASSESSMENT AT YUCCA MOUNTAIN PART II: EARTH SCIENCE AND ENGINEERING FACTORS IN PERFORMANCE ASSESSMENT AT YUCCA MOUNTAIN 85 Release from the waste form 85 81 Transport from canisters to the near-field unsaturated zone ................................ Gas phase transport from the unsaturated zone to the 86 atmosphere above Yucca Mountain 87 Atmospheric circulation leading to dispersal of gaseous radionuclides in the world atmosphere 88 Aqueous phase transport from the unsaturated zone to the water table 88 Saturated zone transport from the aquifer beneath the repository to other locations from which water may be extracted by humans or ultimately reach the surface in a regional discharge area Grn~l'~1 ~nr1 Fni~n(lic, N~tl~rn1 Morlif;er~ Climate change Seismicity . . . 90 91 91 92

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TABLE OF CONTENTS Volcanism . . . . XIZI 94 PART III: EXPOSURE SCENARIOS rN PERFORMANCE ASSESSMENT 95 Selection of Exposure Scenarios for Performance Assessment Calculations 97 Exclusion Zone 103 CHAPTER 4 - HUMAN INTRUSION AND INSTITUTIONAL CONTROLS ....................................... ENTRODUCTION .................................. The Consequences of Intrusion .................... Technical basis ........................... Consequence-based analysis ........... 105 105 109 110 111 ADDITIONAL BASES FOR OUR RECOMMENDATION . . 1 13 Categories of Future Human Intrusion Events 1 14 Categories of Hazards Resulting From an Intrusion . . . 1 14 CHAPTER 5 - IMPLICATIONS OF OUR CONCLUSIONS COMPARISON WITH 40 CFR 191 .................... Considerations Generic vs. site-specific standards ............. Dose vs. risk ............................. Differences From 40 CFR 191 117 117 118 118 118 119 Time period 1 19 Population health effects and release limits 120 Human intrusion 120 .................... 121 ............... 121 122 122 122 123 123 124 125 125 126 Ground-water protection Common Elements With 40 CFR 191 Dose apportionment ....................... R~f~r~nr~hin~nh~re 4~_~_. _.,__ va~v~_^ _ .. . . . . . . . .. . ... . . . . .. . . Exclusion zone ........................... Use of mean values ........................ LIMITS OF THE SCIENTIFIC BASIS TECHNOLOGY-BASED STANDARDS The Al AD ~ PrinrinlP 1 11~ ~l~f11~ 1 1 Il1~ .......................... 10 CFR 60 ........................................ Minimum Early Release ......................... ADMINISTRATIVE CONSEQUENCES FOR EPA, USNRC, AND DOE ................................... 127

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XIV YUCCA M O UNTAIN STA NDAh1)S APPENDIX A - BIOGRAPHICAL INFORMATION ON COMMITTEE MEMBERS 129 APPENDW B - CONGRESSIONAL MANDATE FOR THIS REPORT ................................... APPENDIX C - A PROBABILISTIC CRITICAL GROUP APPENDIX D - THE SUBSISTENCE-FARMER CRITICAL GROUP ................... 1 135 145 153 APPENDIX E - PERSONAL SUPPLEMENTARY STATEMENT OF THOMAS H. PIGFORD 161 REFERENCES FOR APPENDIX E 182 APPENDIX F - THE COMMITTEE CHAIR'S PERSPECTIVE ON APPENDIX E 187 GLOSSARY . . REFERENCES . ....... 189 199

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TABLE OF CONTENTS List of Figures Figure 1.1 Map showing location of Yucca Mountain region adjacent to the Nevada Test Site in southern Nevada. Figure 1.2 Schematic cross section of the potential Yucca Mountain repository region showing location of the repository horizon and static water table with respect to the thermal/mechanical stratigraphic units Figure 3.1 The Basic Steps in Performance Assessment xv 24 ....... 25 ....... 74 Figure 3.2 Schematic illustration of the major pathways from a repository at Yucca Mountain to humans 82 List of Tables Table 2-1 Average Amounts of Ionizing Radiation Received Yearly by a Member of the U.S. Population ..... ... 38 Table 2-2 Estimated Frequencies of Radiation-Induced Fatal Cancers, Nonfatal Cancers, and Severe Hereditary Disorders, Weighted for the Severity of their Impacts on Affected Individuals ...... 39 Table 2-3 Quantitative High-Level Waste Disposal Objectives/Criteria at International Level and in OECD Countries ............. 43 Table 2-4 Comparison of the Annual Individual Risks Associated with USNRC and EPA Standards 50

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