Immobilization of excess weapon plutonium: A better alternative to glass

The United States plans to immobilize several metric tons of excess weapons plutonium in a solid matrix. The selected material must achieve the short-term goal of deterring proliferation through theft or host-nation reuse, and the long-term goal of preventing plutonium exposures over geologic time. The Department of Energy, after internal review, has recently decided on Synroc, a crystalline ceramic, to immobilize the plutonium. This paper presents an independent technical comparison of glass versus ceramic immobilization options, and reaches similar conclusions to those of the Department of Energy. On a technical basis, Synroc performs better than glass in a number of areas. It is more proliferation resistant than glass due to the more complicated and less well-known extraction process that would be required to separate the plutonium. Synroc is more chemically durable than borosilicate glass and can dissolve more depleted uranium than glasses to address future criticality problems. Now that the Department of Energy has selected Synroc as the waste form of choice for plutonium disposition, it should also be reconsidered for immobilization of high-level nuclear waste.

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