Iron phosphate glass for immobilization of 99Tc

Technetium-99 (Tc-99) can bring serious environmental threats because of its long half-life (tau(1/2) = similar to 2.1 x 10(5) years), high fission yield (similar to 6%), and high solubility and mobility in the ground water. The high volatility makes it difficult to immobilize Tc-99 in continuous melters vitrifying Tc-99-containing nuclear wastes in borosilicate glasses. This work explores a possibility of incorporating a high concentration of Tc-99, surrogated by the non-radioactive Re, in an iron phosphate glass by melting mixtures of iron phosphate glass frits with 1.5-6 mass% KReO4 at similar to 1000 degrees C. The retention of Re achieved was similar to 1.1 mass%. The normalized Re release by the 7-day Product Consistency Test was <10(-2) g/m(2). Surprisingly, the Re escaped from the melt within a short time of heating, especially when the temperature was increased. Therefore, Tc-99 volatilization would still be a challenging task for its immobilization in iron phosphate glasses. (C) 2013 Elsevier B.V. All rights reserved.