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Study on Chemical Durability of Vitrified High Level Waste in Borosilicate Glass Matrix

Tabatabaee Moradi, Haniyeh | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55081 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Samadfam, Mohammad; Sepehrian, Hamid; Yadollahi, Ali
  7. Abstract:
  8. As nuclear energy continues to be used as a useful energy resource, waste management, especially management of high-level nuclear waste (HLW), will always be a major concern, as the future generations should not be deprived of the valuable benefits of this energy. Vitrification of liquid high-level radioactive waste (HLW) has received greater attention, worldwide, than any other high-level waste solidification process. The high solubility of HLW in borosilicate glass, the controllable temperature of this type of glass and its low leaching rate in repository environment, have introduced borosilicate glass as a suitable host for HLW immobilization. In this project, the immobilization of the simulated non-radioactive composition of HLW in a borosilicate glass matrix was investigated. For this purpose, the effect of waste loading (15-30 wt%), borosilicate glass frit (70-85 wt%) and melting process temperature (1150-1250 °C) was investigated using the combined design of experiment method. Waste forms were characterized by XRD, SEM and EDX analyzes. The chemical stability of glass waste forms was also evaluated by the MCC3 standard leaching test (PCT) for cesium, silicon and boron. The studies showed that the samples prepared at 1150 °C with waste loading of 15-30 wt% and also the samples containing 30 wt% waste prepared at 1150-1250 °C temperature had crystalline phase of Britholite and were heterogeneous chemically and structurally. The density of all prepared waste forms was measured in the range of 2-3.5 g/cm3 and the relative volume reduction ratio of waste forms was obtained in the range of 88-73%. According to the obtained results, with increasing temperature and waste loading, the density and volume reduction ratio increased. Studies showed that the glass composition containing 26.25 wt% waste and 73.75 wt% borosilicate glass frit, prepared at 1175°C provides the best conditions for waste immobilization, while normalized leaching rate of cesium, silicon and boron obtained in the range of 2.44×10-3, 3.58×10-3 and 9.83×10-3 g/m2.day. Also, the density and relative volume reduction ratio of the sample prepared in the optimal condition were measured 2.737 g/cm3 and 86.258%, respectively
  9. Keywords:
  10. Durability ; Chemical Durability ; Immobilization in Glass ; Borosilicate Glass ; High-Level Nuclear Waste (HLW) ; Simulated Non-Radioactive Waste ; Design of Experiments Method(DOE)

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