Evaluation of physicochemical characteristics and centerline temperatures of Sr ceramic waste form

When disposing of spent fuel, nuclides such as Cs-137 and Sr-90, which generate short-term decay heat, must be removed from the spent nuclear fuel for efficient storage facility utilization. The Korea Atomic Energy Research Institute (KAERI) has been developing a nuclide management process that can enhance disposal efficiency by sorting and collecting primary nuclides and a technology for separating Sr nuclides from the spent nuclear fuels using precipitation and distillation. In this study, we prepared Sr ceramic waste form, SrTiO₃, using the solid-state reaction method to immobilize the Sr nuclides, and its physicochemical properties were evaluated. Moreover, the radiological and thermal characteristics of the Sr waste form were evaluated by estimating the composition of Sr nuclides considering the spent nuclear fuel history such as burn-up and cooling period. The waste form was found to be stable with good mechanical strength and leaching properties in addition to a low coefficient of thermal expansion, which would be advantageous for intermediate storage. Based on the experimental and radiological results, the centerline temperature of the waste form caused by Sr-90 nuclide was estimated using the steady-state conduction equation. The centerline temperature increased with increasing diameter of the waste form. When generating the SrTiO₃ waste form using the Sr nuclide recovered after a cooling period of 10 years, the centerline temperature was estimated to exceed the melting point of SrTiO₃ at a diameter of 0.275 m, under all burn-up conditions. These results provide fundamental data for the management and intermediate storage of Sr waste.