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Glass as a Waste Form and Vitrification Technology: Summary of an International Workshop 3 Special Applications of Glass At least pertaining to issues in the United States, several cases were discussed at the workshop in which vitrification is being considered or used for new and special applications. 1. At the Savannah River Site, a pilot plant has been built to vitrify americium and curium to provide a safe package in which to transfer the material to Oak Ridge National Laboratory for later use. Processing is scheduled to begin in 1998. In this case the glass must provide a safe package rather than serve as a long-term barrier. The glass must be mechanically and thermally stable for a short time and relatively easily dissolved in order to recover the americium and curium. Savannah River also is evaluating this process for the vitrification of neptunium and plutonium solutions. Processing for the americium and curium and also for the neptunium (due to protactinium-233 in growth) must be done in a hot cell. 2. The United States and Russia have an increasing amount of weapons-grade plutonium recovered from dismantled nuclear weapons. Several options are being considered for disposition of this material. The principal options are those recommended in Management and Disposition of Excess Weapons Plutonium: Reactor-Related Options of the National Academy of Sciences (1995). The purpose of all options is to make it as difficult to obtain the weapons plutonium as it is to extract it from reactor spent fuel. This is the "spent fuel standard" developed in another report, Management and Disposition of Excess Weapons Plutonium (National Academy of Sciences, 1994). One of the preferred options is to mix the plutonium with high-level waste and vitrify the mixture. In this case the purpose of the glass is to immobilize both the plutonium and the radioactive waste in a form that makes it difficult to extract the plutonium. In addition to the repository-type criteria for the high-level waste glass (e.g., durability), the plutonium itself introduces additional complications, primarily related to concerns for criticality. The melter process must not lead to an accumulation of a critical mass of plutonium (4 to 10 kg), and the glass should not release sufficient plutonium during long-term alteration of the glass such that precipitation and concentration lead to criticality. These issues have not been examined sufficiently, at least in the United States, to conclude what plutonium loading is possible or should be used. The "can-in-canister" approach was mentioned at the workshop, a subject about which many questions remain to be addressed, including whether it meets the "spent fuel standard." With this concept, small cans of plutonium-loaded glass are placed in a larger canister that is filled with a glass containing HLW. The high level of radioactivity from the HLW glass prevents easy handling of the canister and reduces the retrievability of the plutonium.
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