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Experimental Study of Drying and Calcination of Simulated High-Level Waste (HLW)

Farahzadi, Zahra | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56399 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Samadfam, Mohammad; Zahakifar, Fazel; Zaheri, Parisa
  7. Abstract:
  8. One of the novel methods of stabilization of nuclear waste is the use of vitrification technology. In order to stabilize high level wastes (HLLW) in glass, it is required that the elements are in their oxide form. Therefore, it is necessary to evaporate the waste and turn it into a solid form so that the elements can be converted into oxide form in the calcination furnace. Hence, one of the challenges of stabilization is the optimization of evaporation and calcination conditions. In this research, the parameters affecting evaporation were first investigated. Using laboratory measurements of application: temperature (110 to 180 °C), presence of nitric acid (0.5 to 4 mol/L), ratio of zirconium to molybdenum (0, 1.5, 3), presence of all components (0, 50 and 100 g/L), additives including sugar and azodicarbonamide (10 and 20% by weight each) and a combination of sugar and azodicarbonamide (10% by weight) and the effect of mass transfer surface (8.0384, 11.61, and 16.335 cm2). were investigated as important process applications on simulated liquid waste evaporation (HLLW). The results showed that the evaporation rate depends on the temperature and the evaporation time decreases with the increase of the experiment temperature. The mass-time curves showed that the process of evaporation of the HLLW simulated waste solution consists of two zones of evaporation of the solution and drying of the paste-like material, where the maximum evaporation rate occurs in the zone of evaporation of the solution. Also, at the beginning of the process when the temperature increase is significant the evaporation rate was at its maximum amount. The results showed that zirconium and molybdenum sediments had a negligible effect on the evaporation process of the simulated HLLW solution, and the evaporation time increases with the increase in the concentration of the total components. Also, the addition of azodicarbonamide decreased the evaporation time and increased the mass transfer rate. Addition of sugar did not cause a big difference in the mass change rate in the initial times, but the total evaporation time decreased and improved the physical properties of the product.
    Also, the experiments showed that the batch calcination of the simulated HLLW solution takes place at a temperature of 650 degrees Celsius, and temperatures higher than that cause sublimation of the elements. The addition of azodicarbonamide had a greater effect than the addition of sugar, and adding it up to 20% caused a thermal decomposition of 86%. In the continuous mode (rotary furnace), the effect of the residence time, slope, temperature, and addition of sugar were investigated. The results showed that the calcination rate increases with the decrease of the residence time slope, and with the increase of the amount of sugar, the fluidity of the product increases, and the highest amount of sodium nitrate calcination occurs at 750 degrees Celsius
  9. Keywords:
  10. High-Level Nuclear Waste (HLW) ; Immobilization in Glass ; Evaporation ; Rotary Kilns ; Calcination ; Simulated Liquid Waste

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