Evaluation of thermal stability in deep geological repository and nuclear criticality safety of spent nuclear fuel vitrified in iron phosphate glass

Abstract Iron phosphate glasses with low melting temperatures of ∼1300 °C were developed to immobilize spent nuclear fuels (SNFs). The glasses have densities of ∼3.15 g/cm3 and glass transition temperatures of ∼540 °C that are high enough to endure the temperatures in geological repositories. The waste loading of CeO2 in the glass was ∼21.92 wt%, which corresponds to ∼30.38 wt% of UO2 at the same molar ratio. Normalized elemental releases from the product consistency test were well below the regulated limit of 2 g/m2. Effective neutron multiplication factor keff was 0.755, which is below nuclear criticality safety regulation (keff = 0.95). Vitrified SNF occupies one-eleventh of the repository space compared to direct disposal of the same amount of UO2, excluding left-over low-level wastes.