H-Canyon and HB-Line are tasked with the production of plutonium oxide (PuO 2) from a feed of plutonium (Pu) metal. The PuO 2 will provide feed material for the Mixed Oxide (MOX) Fuel Fabrication Facility. After dissolution of the Pu metal in H-Canyon, plans are to transfer the solution to HB-Line for purification by anion exchange. Anion exchange will be followed by plutonium(IV) oxalate precipitation, filtration, and calcination to form PuO 2. The filtrate solutions, remaining after precipitation, contain low levels of Pu ions, oxalate ions, and may include solids. These solutions are transferred to H-Canyon for disposition. To mitigate the criticality concern of Pu solids in a Canyon tank, past processes have used oxalate destruction or have pre-filled the Canyon tank with a neutron poison. The installation of a filter on the process lines from the HB-Line filtrate tanks to H-Canyon Tank 9.6 is proposed to remove plutonium oxalate solids. This report describes SRNL's efforts to determine the appropriate pore size for the filters needed to perform this function. Information provided in this report aids in developing the control strategies for solids in the process. The tests performed during this effort report the following results.  Percent losses to the filtrate were < 1% for four of five tests and 1.5% for one test.  Sub-micron particle sizes are retained by initial filtration using a 10 μm filter. The filter cake aids in the filtration of the smaller particles.  The mean particle size increases with an increase in the initial acid concentration.  Larger mean particle sizes were observed when changing from a nitric acid/oxalic acid flush to nitric acid alone.  The size of Pu oxalate particles in HB-Line filtrate solutions averages 2.0 ± 0.4 μm in range of precipitation conditions tested. Further development of the "filter the filtrate" strategy must be geared to retain particles of the 2 μm size range.