Legacy ponds at the Sellafield site have been used to store historic radioactive waste for decades, and progress is being made in reducing the risks associated with these facilities. Over time, there has been a deterioration in the condition of the ponds and their contents, which has resulted in particles being present in solution in the ponds. It is important to characterise these particles, whose size are believed to range in diameter from nanometres to microns, in order to facilitate further reductions in the risks.
Commercially-available instrumentation is capable of assessing the size and number of particles in a solution, based on their motion, when the particles have diameters larger than about 150nm; however, recent research has shown that particles with smaller diameters exhibit different behaviour leading to erroneous measurement results in these instruments.
At low concentrations, the motion of nanoparticles with diameters less than about 150nm has been found to be independent of their size, density and material. These findings were obtained by tracking particles using the three-dimensional optical signature, or caustic, which they generate in an optical microscope, these can be several orders of magnitude larger than the particle. In this project, it is proposed to extend this work by developing an instrument that is capable of assessing the number and size of small nanoparticles in a solution representative of those recovered from the legacy ponds at Sellafield.
The research will be undertaken using existing facilities at the University of Liverpool, initially using simple solutions and then progressing to non-radioactive simulants of the pond solutions. The long-term goal is to transition the technology to the Sellafield site and, hence, the final stage of the PhD project will be to demonstrate the technology on pond solutions using the facilities of the National Nuclear Laboratory.
The programme is funded by EPSRC, industrial partners and participating institutions.