Release of Neptunium from Neptunium-Doped Borosilicate Waste Glass

Abstract

The release of neptunium from a neptunium-doped borosilicate waste glass was studied at 90°C in deionized water and silicate water. The standard MCC-1 static leach method was applied to the tests for durations up to 91 days with the SA/V ratio of 10 m^-1.
The normalized elemental mass loss obtained for neptunium was about 5 g/m² for both the deionized and the silicate water leachates. This value is similar to those for currently typical borosilicate waste glasses. That is, the studied glass is comparable with the typical glasses in terms of the ability to immobilize neptunium.
The time dependence of the release of neptunium from the glass was different from those of soluble glass components such as sodium, boron and cesium, but similar to that of strontium. A part of neptunium, like strontium, probably remained in the surface layer formed on the leached glass. The neptunium species in the surface layer was predicted to be NpO₂•xH₂O(am) based on available solubility data.