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EvnIuntion of the U.S. Department of Energy's Alternatives for the Removal and Disposition of Molten Salt Reactor Experiment Fluoride Salts Molten Salt Panel of the Committee on Remediation of Buried and Tank Wastes Board on Radioactive Waste Management Commission on Geosciences, Environment, and Resources National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1997

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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 from 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 the 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 was provided by the U.S. Department of Energy under Grant No. DE-FC01-94EW54069. All opinions, findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of the U.S. Department of Energy. Library of Congress Catalog Card Number 96-72354 International Standard Book Number 0-309-05684-5 Additional copies of this report are available from: National Academy Press 2101 Constitution Avenue, N.W. Box 285 Washington, DC 20055 800-624-6242 202-334-3313 (in the Washington Metropolitan Area) http://www.nap.edu Copyright 1997 by the National Academy of Sciences. All rights reserved. Cover: The cover shows a drawing of one of the drain tanks of the Molten Salt Reactor Experiment that contains a solidified mixture of radioactive fluoride salts. The top section, attached to bayonet-like thimbles that penetrate the bottom section, was designed for cooling water to absorb heat from the tank contents. The background shows a ternary phase diagram for the three main ingredients of the fluoride saltslithium fluoride (LiF), beryllium fluoride (BeF2), and zirconium fluoride (ZrF41. The dark green color is the true color of solid uranium tetrafluoride (llF4), also present in the salts. Special thanks to Mary Catlin for digitizing the figures from Peretz (1996c) for this artwork. Printed in the United States of America

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MOLTEN SALT PANEL OF THE COMMITTEE ON REMEDIATION OF BURIED AND TANK WASTES JOHN L. MARGRAVE, Chair, Rice University, Houston, Texas SOL BURSTEIN, Wisconsin Electric Power, Milwaukee (retired) ROBERT J. CATLIN, University of Texas Health Science Center, Houston (retired) GREGORY R. CHOPPIN, Florida State University, Tallahassee MELVIN S. COOPS, Lawrence Livermore National Laboratory, California FLOYD L. CULLER, JR., Electric Power Research Institute, Inc., Palo Alto, California (emeritus) ALBERT W. JACHE, Marquette University, Milwaukee, Wisconsin (emeritus) RONALD KNIEF, Ogden Environmental and Energy Services, Albuquerque, New Mexico MILTON LEVENSON, Bechtel International, San Francisco, California (retired) ROBERT A. PENNEMAN, Los Alamos National Laboratory, New Mexico (retired) ROBERT A. RAPP, Ohio State University, Columbus (emeritus) EDWIN L. ZEBROSKI, Aptech Engineering Services, Inc., Sunnyvale, California Consultants VALERIE PUTMAN, Lockheed Martin Idaho Technologies Company, Idaho Falls THOMAS A. REILLY, Westinghouse Savannah River Company, Aiken, South Carolina NRC*taff THOMAS E. KIESS, Study Director REBECCA BURKA, Senior Project Assistant ERIKA L. WILLIAMS, Project Assistant . . .

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COMMITTEE ON REMEDIATION OF BURIED AND TANK WASTES THOMAS M. LESCHINE, Chair, University of Washington, Seattle DENISE BIERLEY, Roy F. Weston, Albuquerque, New Mexico ROBERT J. BUDNITZ, Future Resources Associates, Berkeley, California THOMAS A. BURKE, The Johns Hopkins University, Baltimore, Maryland ROBERT J. CATLIN, University of Texas, Houston (retired) GREGORY R. CHOPPIN, Florida State University, Tallahassee JAMES H. CLARKE, Eckenfelder, Inc., Nashville, Tennessee THOMAS A. COTTON, JK Research Associates, Inc., Arlington, Virginia ALLEN G. CROFF, Oak Ridge National Laboratoly, Tennessee DONALD R. GIBSON, JR., TRW Environmental Safety Systems, Vienna, Virginia JAMES H. JOHNSON, JR., Howard University, Washington, D.C. W. HUGH O'RIORDAN, Givens Pursley & Huntley, Boise, Idaho GLENN PAULSON, Paulson and Cooper, Inc., Jackson Hole, Wyoming BENJAMIN ROSS, Disposal Safety Incorporated, Washington, D.C. PAUL A. WITHERSPOON, University of California, Berkeley RAYMOND G. WYMER, Oak Ridge National Laboratory, Tennessee (retired) NRC Staff ROBERT S. ANDREWS, Senior Staff Officer DENNIS L. DuPREE, Senior Project Assistant PATRICIA A. JONES, Senior Project Assistant iv

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BOARD ON R\DlOACTlVE WASTE MANAGEMENT MICHAEL C. KAVANAUGH, Chair, Malcolm Pirnie, Inc., Oakland, California B. JOHN GARRICK, Vice-Chair. PLG, Inc., Newport Beach, California JOHN F. AHEARNE, Sigma Xi, The Scientific Research Society, and Duke University, Research Triangle Park and Durham, North Carolina JEAN M. BAHR, University of Wisconsin, Madison SOL BURSTEIN, Wisconsin Electric Power, Milwaukee (retired) ANDREW P. CAPUTO, Natural Resources Defense Council, Washington, D.C. MELVIN W. CARTER, Georgia Institute of Technology, Atlanta (emeritus) PAUL P. CRAIG, University of California, Davis (emeritus) MARY R. ENGLISH, The University of Tennessee, Knoxville DARLEANE C. HOFFMAN, Lawrence Berkeley Laboratory, Berkeley, California JAMES H. JOHNSON, JR., Howard University, Washington, D.C. CHARLES McCOMBIE, NAGRA, Wettingen, Switzerland ROBERT MEYER, Keystone Scientific, Inc., Fort Collins, Colorado D. WARNER NORTH, Decision Focus, Inc., Mountain View, California PAUL SLOVIC, Decision Research, Eugene, Oregon BENJAMIN L. SMITH, Independent Consultant, Columbia, Tennessee NRC Staff KEVIN D. CROWLEY, Director ROBERT S. ANDREWS, Senior Staff Officer KARYANIL T. THOMAS, Senior Staff Officer THOMAS E. KIESS, Staff Officer SUSAN B. MOCKLER, Research Associate LISA J. CLENDENING, Administrative Associate ROBIN L. ALLEN, Senior Project Assistant REBECCA BURKA, Senior Project Assistant DENNIS L. DuPREE? Senior Project Assistant PATRICIA A. JONES, Senior Project Assistant ANGELA R. TAYLOR, Project Assistant ERIKA L. WILLIAMS, Research Assistant v

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COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES GEORGE M. HORNBERGER, Chair, University of Virginia, Charlottesville PATRICK R. ATKINS, Aluminum Company of America, Pittsburgh, Pennsylvania JAMES P. BRUCE, Canadian Climate Program Board, Ottawa, Ontario WILLIAM L. FISHER, University of Texas, Austin JERRY F. FRANKLIN, University of Washington, Seattle THOMAS E. GRAEDEL, Yale University, New Haven, Connecticut DEBRA KNOPMAN, Progressive Foundation, Washington, D.C. KAI N. LEE, Williams College, Williamstown, Massachusetts PERRY L. McCARTY, Stanford University, California JUDITH E. McDOWELL, Woods Hole Oceanographic Institution, Massachusetts RICHARD A. MESERVE, Covington & Burling, Washington, D. C. S. GEORGE PHILANDER, Princeton University, New Jersey RAYMOND A. PRICE, Queen's University at Kingston, Ontario THOMAS C. SCHELLING, University of Maryland, College Park ELLEN SILBERGELD, University of Maryland Medical School, Baltimore VICTORIA J. TSCHINKEL, Landers and Parsons, Tallahassee, Florida E-AN ZEN, University of Maryland, College Park NRC Staff STEPHEN RATTIEN, Executive Director STEPHEN D. PARKER, Associate Executive Director MORGAN GOPNIK, Assistant Executive Director GREGORY SYMMES, Reports Officer JAMES MALLORY, Administrative Officer SANDI FITZPATRICK, Administrative Associate MARQUITA SMITH, Administrative Assistant/Technology Analyst Vl

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Acknowledgments The pane! is especially appreciative of the support of Dr. Tom Kiess, Ms. Rebecca Burka, and Ms. Erika Williams in collecting, assembling, and organizing the input from our group into a coherent format. We also wish to acknowledge the cooperation of the management and staff of the Oak Ridge National Laboratory and of the Department of Energy in providing information for this report. The assistance of Ray Wymer, a liaison to the panel from the Committee on Remediation of Buried and Tank Wastes, is gratefully acknowledged. The early assistance of Dr. lames Zucchetto, Director of the National Research Council Board on Energy and Environmental Systems, and Dr. Douglas Raber, Director of the National Research Council Board on Chemical Science and Technology, is much appreciated. . . Vll

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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. William A. Wulf is interim president of the National Academy of . . _nglneerlng. 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. William A. Wulf are the chairman and interim vice-chairman, respectively, of the National Research Council. . . . vail

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Preface More than 25 years ago, I was a consultant to the group that was designing, building, and operating the Molten Salt Reactor Experiment (MSRE). Now the "mothballed" MSRE presents an environmental hazard that must be remediated soon, and I have been appointed to chair a National Research Council study of the remediation alternatives under consideration. The fluoride salts that were once the reactor fuel and that are now stored in drain tanks have been unstable since the reactor was shut down in 1969. The potential hazards of the toxic, radioactive, and fissionable materials have been extensively reviewed since the early 1970s and are worsening with time. This report describes the scientific and engineering aspects of feasible remediation plans for the fluoride salt contents of the three drain tanks of the facility. The panel has carefully reviewed the previous studies and the recent technical evaluations of the alternatives proposed by staff at the Oak Ridge National Laboratory (ORNL). The panel was impressed with the information and background knowledge available at ORNL and from other Department of Energy (DOE) sites, including that from retirees who had run the reactor and who had developed the basic fluoride chemistry. At the present time, DOE has provided funding and personnel to take action on this environmental hazard. Many ORNL staff and now members of the public recognize the high priority of this remediation project. The panel supports the completion of remediation work on this cleanup problem that the present DOE management has inherited and has the opportunity to solve. John L. Margrave Houston, Texas zx

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Contents Executive Summary 1 Introduction Current Status of the MSRE, 15 Role of the National Research Council, 19 Scope and Organization of This Report, 20 2 Radiolysis and Nuclear Reactions Radioactive Source Terms, 23 Radiation Effects and General Comments, 27 Radiation-Induced Liberation of Fluorine and Uranium Hexafluoride Gases, 28 Radiation Decomposition of Solid Uranium Hexafluoride, 31 Long-Term Effects of Leaving Plutonium in the Salt After Uranium Removal, 33 Excess of Reducing Species in the Salt and Hazards of Simple Remelting, 34 3 Fluoride Salt Chemistry, Partitioning, and System Corrosion Chemistry Relevant to the Present Status, 37 Chemical Consequences of RadioTysis, 38 Partitioning of Uranium from the Salt, 39 Plutonium Partitioning by Fluorination, 41 Nonfluorination Option for Plutonium Separation, 42 System Corrosion Issues, 42 Radiation-Tnduced Corrosion Questions, 43 1 10 23 37 4 Preferred Technical Approach 45 Comments on Process Steps, 45 Development of a Preferred Approach, 46 Xl

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. . X11 Comments on Specific Separation Technologies Fluorination, 50 Direct Fluorination, 51 Hydrofluorination, 52 Alternative Fluorinating Agents, 52 Electroref~ning, 53 Distillation of Molten Salt, 54 Aqueous Dissolution and Separation, 54 Criticality Concems in Aqueous Processing, 55 Fluoride Removal, 56 Conclusions on Aqueous Processing, 56 Stabilization Technologies, 57 6 Nuclear Criticality Considerations Criticality Issues in Processing, 58 Criticality Hazard of Remelting the Fluoride Salts in the Drain Tanks, 6 1 CONTENTS 50 58 Rationale for Technical Insignificance of a Criticality Excursion, 63 Concluding Comments, 64 7 Strategic Alternatives Permanent Disposal in the Drain Tanks, 65 Disposal of All Key Contaminants in the Federal Repository, 65 Disposal of Key Contaminants in the Salt Residue in the Waste Isolation Pilot Plant (WIPP), 66 Disposal of Key Contaminants in Salt Residue in the Federal Repository, 67 Reuse of the Salt, 68 Interim Storage, 68 Rationale for Rejecting the First Six Alternatives, 69 Interim Versus Permanent Storage and Disposal, 70 Management of MSRE Hazards Current Hazards, 72 Hazard Management Activities, 74 65 72

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CONTENTS Crucial Role of Further Activities for Condition and Process Assessment' 74 Major Recommendation Concerning Hazards, 75 Detailed Recommendations Regarding Hazards, 76 9 Summary and Responses to Questions in Statement of Task Technical Summary, 79 Strategy for Remediation, 81 Where is the Uranium? 81 How Can a Condition Assessment Affect Remediation Plans? 82 The Panel's Preferred Alternative, 83 Hazards, 83 Responses to Questions in Statement of Task, 84 Question 1, 84 Question 2, 85 Question 3, 86 Panel Perspective, 87 Overall Conclusion, 88 References Appendixes A List of Materials Reviewed B Alternative Fluorinating Agents C Contamination Concerns Relating to Radon Gas Spread D Use of a Nuclear Poison to Inhibit Nuclear Criticality . . . x~ 79 89 A.1 B.1 C.1 D.1 E Hazard Scoping of Major Actions for Remediation E.1

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XIV F List of Acronyms and Abbreviations G Glossary H Biographical Sketches of Molten Salt Pane} Members and Consultants CONTENTS F.1 G.1 H.1