Iron phosphate glass for immobilization of 99Tc

•99Tc (surrogated by Re) was immobilized in an iron phosphate glass.•∼1.1 mass% Re was retained, possibly dissolved, in the iron phosphate glass.•The 7-day PCT normalized release of Re was <10−2 g/m2.•Re concentration in the glass rapidly decreased with increasing melting temperature and duration.

Technetium-99 (99Tc) can bring serious environmental threats because of its long half-life (τ1/2 = ∼2.1 × 105 years), high fission yield (∼6%), and high solubility and mobility in the ground water. The high volatility makes it difficult to immobilize 99Tc in continuous melters vitrifying 99Tc-containing nuclear wastes in borosilicate glasses. This work explores a possibility of incorporating a high concentration of 99Tc, 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 ∼1000 °C. The retention of Re achieved was ∼1.1 mass%. The normalized Re release by the 7-day Product Consistency Test was <10−2 g/m2. Surprisingly, the Re escaped from the melt within a short time of heating, especially when the temperature was increased. Therefore, 99Tc volatilization would still be a challenging task for its immobilization in iron phosphate glasses.