Finally, despite many years of development and large investments in nuclear waste solidification, the present technologies are essentially of only two types; a single-stage liquid-fed ceramic melter and a two-stage rotating calciner and a metallic melter, both producing a borosilicate glass. Are there new technologies? Are there other waste forms? Furthermore, vitrification plants are expected to be operational for the next 30 to 50 years. As in any large-scale industrial endeavor, both the process and the product will certainly be improved with time. Any plant modifications must be based both on practical operational experience and a sound scientific understanding of fundamental issues and phenomena. The National Research Council (NRC) workshop was aimed at identifying and discussing these underlying fundamental issues.

Given the scale and complexity of the task of vitrifying nuclear wastes, it is prudent to review the past 30 years of successes and failures and to use this knowledge to plan an efficient path for the very large job ahead. Future plans should reflect the best application of processing technologies and a knowledge of waste forms that reduces risk to the public and the environment while also avoiding unnecessary cost and delay.

In light of the above, the NRC Board on Radioactive Waste Management decided that it was timely to convene an International Workshop on Glass as a Waste Form and Vitrification Technology. The DOE Waste Management Program provided financial support and logistical assistance for the workshop. A general goal of the workshop was to review the current state of knowledge of glass as a waste form for the immobilization of radioactive wastes. The workshop was held on May 13-15, 1996, in the auditorium of the National Academy of Sciences in Washington, D.C., and was attended by approximately 250 participants (see Appendix C) representing 12 countries. The workshop program, given in Appendix B, included sessions on the Present Status of Vitrification, Glass Durability and Modeling, and Operational Experiences with Vitrification, as well as posters, panel discussions, and summaries by rapporteurs. This report summarizes some of the major discussions of the workshop from the perspective of the steering committee; extended abstracts of the presentations are included in Appendix E.

A three-day program cannot capture the detail of highly specialized waste management meetings held around the world (of which there are many; specifically the reader is referred to the proceedings of the Materials Research Society's annual symposium on the Scientific Basis for Nuclear Waste Management, the biennial symposium of the American Society of Mechanical Engineers, and the annual Waste Management meetings held in Tucson, Arizona). The NRC workshop was not intended to be an exhaustive review of the status of this complex subject, but rather an opportunity to identify remaining critical areas for future research based on presentations by leading international experts in the field. The workshop program (see Appendix B) was constructed around the four following issues that were addressed by the invited speakers.

• Waste Characteristics: What are the volumes, states, and compositions of the waste that might be vitrified?

• Regulations: In the United States, what regulations apply to the waste form, and what is the basis for the regulation?

Front Matter (R1-R10)

Executive Summary (1-2)

1 Introduction (3-7)

2 Three Futures for Glass (8-18)

3 Special Applications of Glass (19-19)

4 Conclusions (20-21)

References (22-24)

Appendix A Biographical Sketches of Committee Members (25-26)

Appendix B Workshop Program (27-30)

Appendix C List of Workshop Participants (31-38)

Appendix D Identification and Summary of Characterization of Materials Potentially Requiring Vitrification (39-52)

Appendix E Abstracts of Invited Workshop and Poster Presentations (53-162)