Influence of doping of NaNO3 on the solid phase thermal decomposition of bitumen and cement

The thermal stability of solidified NaNO3 salts in bitumen and cement has b een investigated for safety considerations in the field of solidification o f radioactive waste. The thermal decomposition of bitumen and cement in pre sence of NaNO3 in a temperature range 22-650 degreesC has been studied. The fraction decomposed of the pure samples and mixtures showed slow linear re actions followed by acceleratory and decay stages. Data are analyzed accord ing to both Freeman-Carroll and Coats-Redfern kinetics to evaluate the acti vation energy and the order of reactions of all mixtures. It is found that the activation energies of bitumen and cement were 594 and 203 kJ mol(-1), respectively. The order of reactions of bitumen and cement was 2 and 4, res pectively. The addition of NaNO3 shortens the duration of the induction per iod in all mixtures. It was concluded that solidification of radioactive wa ste containing NaNO3 in bitumen and cement should be applied in the tempera ture range 22-300 degreesC. At temperature higher than 300 degreesC solidif ication should be in cement.