Aqueous Alteration of Nuclear Waste Glasses and Metal Package Components
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High-Level Radioactive Waste Management in the United States Background In the United States, there are approximately 100 million gallons of high-level radioactive waste containing more than 1 billion curies of radioactivity. This waste is currently being handled and stored predominantly at three main Department of
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Energy (DOE) sites—the Hanford Reservation in Richland, Washington; the Savannah River Site in Aiken, South Carolina; and the Idaho Chemical Processing Plant at Idaho Falls, Idaho. These HLW inventories were produced mainly as a byproduct in the production of nuclear materials used for national defense, and exist in addition to a large and growing inventory of spent fuel used in the production of electricity.1'2 HLW is most often handled and stored in a liquid form with the bulk of this inventory placed in underground tanks, many with a capacity in excess of 1 million gallons. It is important to note that (a) this original "short-term" storage strategy for HLW has been safe and effective for more than a' quarter of a century of operation, and (b) that although this has been effective, a more permanent or long-term solution for immobilizing hazardous radionuclides is still needed.
Why Glass? As the result of about four decades of research and development, glass is the chief international material of choice for immobilizing and ultimately disposing of potentially hazardous high-level radioactive waste.1'2 Glass matrices are also being considered for the immobilization and isolation of a variety of other types of radioactive, as well as nonradioactive, materials. One relatively new application that may be important in the future is the potential use of glassmaking operations for the destruction and subsequent vitrification of weapons
materials and hazardous waste components. There are many factors which contribute to the suitability of immobilizing nuclear and hazardous constituents into glass matrices. These advantages fall into two general areas: (a) outstanding technical performance of waste glass forms, including good versatility, chemical durability, mechanical integrity, and radiation and thermal stability, and (b) ease of fabrication, meaning the vitrification or glassmaking process is well developed and demonstrated.1
Multibarrier Isolation System Many different long-term waste management options, along with a variety of potential waste forms, were studied and evaluated to handle the first waste to be treated in the United States, the HLW at the Savannah River Site (SRS). A methodology was selected that involves removing waste from current storage tanks, separating radioactive from nonradioactive components, chemically processing the waste, and finally, immobilizing radionuclides into borosilicate glass. Construction of a billion-dollar vitrification building, the Defense Waste Processing Facility (DWPF), at SRS has recently been completed. The facility is now undergoing "cold testing," using water and then simulated waste compositions, before going into actual "hot" or radioactive productio
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