Study of radiolysis bubbles in bitumen used for nuclear waste management with ultrasounds and X-Ray microtomography

In the realm of nuclear waste management, an ultrasonic investigation of radiolysis bubbles in bitumen has been carried out. Mechanical waves are very sensitive to gas cavities in matter, therefore ultrasonic velocity was measured in a straight-run distillation bitumen labelled AZALT 70/100 irradiated with 60 Co (gamma irradiation) at dose rates between 5 and 1200 Gy/ h and total integrated doses ranging from 2 to 100 kGy in IRMA and PAGURE French irradiation facilities. A comparative study of ultrasonic velocity and X-Ray microtomography measurements shows that ultrasonic velocity is linked to the concentration of bubbles within the material. A first attempt to deduce the volume fraction of hydrogen bubbles created by irradiation at ambient conditions with ultrasonic velocity measurements are proposed and discussed. This method constitutes an interesting approach dedicated to the monitoring of radiolysis bubbles formation and their evacuation mechanisms. It is particularly promising as ultrasonic sensors can operate effectively in high radiative and high temperature environments. Thus, real time application can be envisaged during irradiation and temperature increase for future experiments.