Rheological investigation of bitumen, used for radioactive waste conditioning, with ultrasonic waves

Abstract

In the context of bituminized radioactive waste storage and disposal, nucleation monitoring at room temperature and radiolysis bubbles migration at elevated temperature is crucial particularly in fire scenarios where bubble may impact thermal properties. Traditional methods are limited by the opacity of bitumen. To gain a deeper insight into bitumen rheology and ultrasonic wave propagation, we conducted a pilot study using ultrasonic testing cells spanning temperatures from 10°C to 60°C. Ultrasonic velocities and attenuations were measured at around 500 kHz in a 70/100 grade bitumen. Rheological information was deduced with the Time-Temperature Superposition principle and a behaviour model was proposed to describe bitumen across a wide frequency range. Notably, our study reveals a transition point around 50°C to 60°C, where bitumen’s liquid behaviour becomes dominant. The shear-thinning characteristics gradually give way to a more Newtonian response. Using the proposed model, ultrasonic attenuation and viscosity were estimated at 110°C. Acceptable ultrasonic frequencies for monitoring the nucleation and migration of radiolysis bubbles are discussed for future investigations. These findings have significant implications for safety measures and a deeper understanding of bitumen response within the realm of radioactive waste management.