EXECUTIVE SUMMARYAs part of the PET (Process Engineering Technology) simulant development program, an investigation was initiated to determine the best method for particle size analysis of both simulant and radioactive sludge slurries using a physical separation method (i.e. sieving) or a laser light diffraction method such as Microtrac or Lasentec. The experiments performed in this investigation were completed with Sludge Batch 3 simulant and radioactive sludge slurries. The long-term goals of the investigation were: (1) to build a database of the size of particles in actual radioactive waste tank sludge and determine the impact of particle size on rheology, and (2) to aid in the development of simulant slurries that closely match the particle size and rheological behavior of radioactive sludge.