Ultrasonic Techniques for the In Situ Characterization of Nuclear Waste Sludges – 11275

Ongoing research at the University of Leeds, being undertaken as part of the DIAMOND university consortium, is exploring the effectiveness of various ultrasonic technologies as in situ probes to characterize and monitor simulant nuclear wastes. Through use of a commercial Ultrasonic Velocity Profiler (UVP) and an Acoustic Backscatter Sensor (ABS) both with 1 – 5 MHz transducers, various properties of free-settling oxide simulant sludges were determined. Work was focused upon characterizing essentially ‘static’ sludges for prospective use within U.K “Legacy” waste sites; although, the sensors have potential as monitors in many storage or thickener/de-watering systems across a wide range of industrial processing operations. The UVP, which correlates particle velocities by measuring the associated frequency Doppler shifts, was able to determine the free-settling rates of sludge particles for a 1-dimensional profile down a settling column, with results highlighting considerable hindered settling effects within certain zones. By focusing on velocity changes in the near bed region, the formation and compaction of the sediment bed over time was also tracked, as well as the movement of the sludge cloud-front. The ABS, which measures the raw attenuation of an ultrasonic pulse through dispersions, was calibrated to measure changes in particulate concentration within a settling suspension, and showed that observed hindered settling also led to an increase in particulate concentration over the sludge zone. Lastly, a quartz crystal microbalance (QCM) probe developed by Rheokinisis was used to track yield stress changes in magnesium hydroxide sludges. Here, changes to the vibrational frequency and electric resistance of a piezoelectric crystal inserted into sludges of various concentrations and at a fixed concentration undergoing consolidation (aging) were measured. Increases to both vibrational frequency and resistance were associated with increases in the sludge matrix yield-stress.