Leaching of Al2O3-Based Nuclear Waste Forms.

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<BR>The chemical durability of LaAlO3 and CaAl12O19 containing simulated high-level waste (HLW) elements (Nd, Ce and Sr) was examined at 90 and 150°C in HCI solution and deionized water. Because of the amphotericity of the major aluminium ions and the high solubility of the other matrix constituents, both waste forms dissolved congruently in HCI solution of pH 1 at 90°C, resulting in high leach rates of more than 10-3g•m-2•d-1 for all constituents. In deionized water, they dissolved incongruently, and leach rates of Al and Nd were less than 10-4g•m-2•d-1. The leach rates in deionized water were lower than those of borosilicate glass waste forms by about 3 orders of magnitude. CaAl12O19 was superior to LaAlO3 in the durability in HCI solution and deionized water. It was found that the leach rates of Nd and Ce from both waste forms decreased with increasing temperature in deionized water. This phenomenon was attributed to the increase of pH resulting from the dissolution of Ca or Sr.
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