NUCLEAR WASTES:

Technologies for Separations and Transmutation

Preface

 Beginning in the 1940s, the U.S. government engaged in a very vigorous program of research, development, and utilization of nuclear energy. One part of the program was focused on the design and production of nuclear weapons. The other part of the effort was focused on the development of nuclear power reactors for both military and civilian use. From the beginning it was clear that use of nuclear energy would result in the generation of considerable amounts of high-level waste, containing radionuclides that are intensely radioactive and/or have long half-lives. Though it was recognized quite early that high-level waste would have to be managed safely without unacceptable risks to humans, for many decades other parts of the nuclear program (including interim storage) were given higher priority. The spent reactor fuel was stored in pools at the reactor site, and the high-level liquid wastes resulting from processing of defense reactor waste were put into underground tanks as temporary solutions to the problem. The age of the oldest of these "temporary" tanks containing processed liquid wastes is now approaching 50 years. Spent civilian-reactor fuel storage has been uneventful, but the high-level waste tanks are corroding and some have developed leaks, creating a hazardous situation. At many reactor sites these storage pools are nearly fulla situation requiring the construction of additional on-site pools or dry storage facilities.

 It is expected that by about 2010 the U.S. civilian nuclear power reactors will have produced about 63,000 Mg (about 70,000 tons) of spent fuel. This will contain about 90% of all high-level radioactive waste in the U.S. nuclear program. The remaining spent fuel will result from the military program.

 Extensive work has been done on research, development, and evaluation of methods for the ultimate safe disposal of this spent fuel and high-level radioactive waste. These studies have almost all concluded that the most practical approach would be to vitrify the liquid high-level wastes in a glass matrix. The resulting glass would then be encapsulated in suitable containers and buried in a specially selected and evaluated stable geological formation deep underground. Present U.S. policy is that spent power reactor fuel would also be encapsulated and buried.

 To implement the disposal process, several recent administrations have announced their intention to establish a national repository for high-level radioactive waste. They developed a program schedule and passed legislation to provide the funding mechanism needed to carry out the program. However, the schedule for the program has been marked by continuous delays, and successive plans have had to be abandoned, resulting in billions of dollars of wasted expenditure. Some reasons for this dilemma are technical, but many are nontechnical. The current stalemate on the Yucca Mountain site in Nevada, sponsored by the U.S. Department of Energy (DOE) is an example of such a case. When Yucca Mountain was identified by the U.S. Congress as the first site to be evaluated, the Nevada governor initiated legal steps to try to stop the federal government from taking any steps to evaluate the site, even though it is on federal property.

 Due to legal interventions such as this, the DOE-sponsored work to establish Yucca Mountain as the first U.S. high-level waste repository is over budget and behind schedule. Still in its investigative phases after many years of effort, it has not yet even been determined if the site is suitable.

 Because of all these difficulties, DOE continues to explore other disposal options that might circumvent such problems. Some of the proposed solutions have focused on separating the hazardous long-lived radioactive nuclides in the waste and transmuting them by neutron bombardment to form nuclides that would be either stable or radioactive with a much shorter half-life. During the last decade, there has been a renewed interest by a few countries in such proposals, and some technological progress has been reported. This has led several of the DOE national laboratories to reexamine this concept to see if it might be put to practical use. Although this approach is technically feasible, its use involves several practical problems a major technical problem is the requirement for production of very high neutron source intensities, which poses severe engineering and material challenges. Another difficult problem is achieving the very high efficiency required in the chemical separation of the radionuclides to be transmuted from the other wastes. Unless high separation efficiency is obtained, full benefits of transmutation may not be achieved. The residual waste may still be contaminated to the extent that it must be considered as high-level waste. In addition to these technical problems, the issues of economics, licensing, and public acceptance present significant obstacles to the adoption of transmutation systems.

 As part of the reexamination of separations and transmutation (S&T) technology systems, in 1991 the Secretary of Energy, Admiral James D. Watkins, Jr., requested the National Research Council (NRC) to conduct a broad systems review of the application of S&T concepts to radioactive waste disposal. To implement this request, the NRC formed a 19-member multidisciplinary committee on Separations Technology and Transmutation Systems (STATS), under the direction of the Board on Radioactive Waste Management. The committee was assisted by a subcommittee on Separations, under the NRC's Board on Chemical Sciences and Technology, and a subcommittee on Transmutation, under the NRC's Board on Energy and Environmental Systems. These subcommittees included 10 additional experts. A third STATS subcommittee on Integration functioned until May 1992.

 The expertise of these committees included engineering, physical and chemical sciences, accelerator physics, radioactive and hazardous waste disposal technologies, health and safety assessment, economics, public and regulatory policies and procedures, and plant operations.

 The scope of the study was to prepare a reviewed report evaluating the relative effects, costs, and feasibility of employing separations and transmutation technologies in the Department of Energy's programs for managing (1) spent nuclear fuel from civilian power reactors, and (2) radioactive wastes in tanks at selected existing defense production reactor sites.

 To initiate the study, an international workshop was held in January 1992, where the committee was briefed on the current status of knowledge in the field by experts representing a wide cross section of disciplines. Following the workshop, the committee undertook an in-depth evaluation of all the aspects concerned with separations technology and transmutation through a number of meetings and briefings. It met with representatives of laboratories and organizations involved with the work and visited their sites in the United States and abroad.

 In May 1992, in response to a request by the Secretary of Energy, an interim report of the committee was submitted that summarized the committee's information at that time concerning actinide burning in advanced liquid-metal reactors and the possible impacts on the repository program.

  The committee examined the currently used "once-through" fuel cycle versus proposed separations technology and transmutation systems for dealing with high-level radioactive waste. Two principal transmutation concepts involving critical reactors, both light-water reactors and advanced fast reactors were examined. In addition, a system was reviewed in which an accelerator combined with a subcritical reactor assembly produced neutrons. The committee also examined in detail the applicability of S&T in the management of defense wastes stored in tanks at the Hanford site.

 This volume constitutes the final report of the STATS Committee. It provides a comprehensive evaluation of separations technology and transmutation technologies, its current status, and some insight on future potential. Associated topics dealing with health, safety, proliferation, socioeconomical, and regulatory issues are covered, as are possible schedules and economics of potential S&T systems. The report further examines whether implementation of S&T concepts can contribute to a safer and more economical waste disposal option than the present "once-through" fuel cycle and waste disposal option.

 The report begins with an Executive Summary followed by a brief introduction to S&T technology in Chapter 1. Chapter 2 gives a description of the technologies involved. Chapters 3 and 4 describe the current status of separations and transmutation technologies, respectively. Some of the issues associated with defense waste are covered in Chapter 5. A number of important issues including licensing, health and safety, proliferation, and economics are reviewed in Chapter 6. Those desiring a more technical discussion will want to refer to Appendices C through K and Appendix P. Because of the frequent use of acronyms, the reader may find Appendix O valuable.

 The STATS report had the benefit of the time and talents of highly professional and dedicated committee members, and it was my privilege and pleasure to work with them on this project. I acknowledge with thanks the many long hours and arduous work they provided in researching, writing, and revising their contributions to the many complex issues involved in separations technology and transmutation systems. Similarly, I extend my appreciation to the Department of Energy, which funded the study and express my appreciation to its staff for their technical support for the committee's work. On behalf of the committee I also express gratitude to the many scientists and engineers representing various organizations and laboratories who briefed the committee and supplied it with the required technical reports dealing with research, development, and evaluation studies on the subject.

 The Subcommittee on Transmutation was chaired by Ed Kintner. The Subcommittee on Separations was chaired by Fred McLafferty. Edward Mason was chairman of the Subcommittee on Integration. My special thanks go to the chairs and members of the subcommittees for their valuable contributions to the STATS committee work.

 John M. Googin, a STATS Committee member, died in January 1994. His vast knowledge in engineering and chemical sciences and extensive corporate memory made his contributions to the STATS Committee invaluable. We grieve his loss.

 The successful conclusion of a study of this magnitude is very dependent on the skills, dedication, and energy of the NRC staff who were assigned to the committee. In particular I thank K.T. Thomas, STATS Study Director and Senior Staff Officer of the Board on Radioactive Waste Management for his many valuable contributions to the study. His pleasant personality, dependability, and talents were responsible for many improvements in the final report. Carl A. Anderson, Director of the Board on Radioactive Waste Management, also made many contributions, particularly to the interim report.

 Thanks also go to James J. Zucchetto, Staff Officer for the Subcommittee on Transmutation, and Scott T. Weidman, Staff Officer for the Subcommittee on Separations, and their respective directors of the two boards, Mahadevan Mani and Douglas J. Raber. Finally, I thank Lisa Clendening, Verna Bowen, and Patricia Jones of the Board on Radioactive Waste Management for their valuable work and guidance in seeing this report through to completion.

Norman C. Rasmussen, Chair

Committee on Separations Technology and

Transmutation Systems

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