Evaluation and Testing of the Cells Unit Crossflow Filter on INEEL Dissolved Calcine Slurries

Development of waste treatment processes for the remediation of radioactive wastes is currently under way at the Idaho Nuclear Technology and Engineering Center (INTEC), located at the Idaho National Engineering and Environmental Laboratory (INEEL). INTEC, formerly known as the Idaho Chemical Processing Plant, previously reprocessed nuclear fuel to retrieve fissionable uranium. Liquid waste raffinates resulting from reprocessing were solidified into a granular calcine material. Approximately 4,000 m3 of calcine are presently being stored in concrete encased stainless steel bins at the INTEC. Greater than 99 weight percent of the calcine is non-radioactive inert materials. By separating radioactive and non-radioactive constituents into high and low activity fractions, a significant high-activity volume reduction can be achieved. Prior to separation, calcine dissolution must be performed. However, dissolution studies have shown a small percentage of solids present after dissolution. Undissolved solids (UDS) in solution must be removed prior to downstream processes such as solvent extraction and ion exchange. Furthermore, residual UDS in solutions have the potential to carry excess radioactivity into low activity waste fractions, if not removed. Filtration experiments were conducted at the INEEL using the Cell Unit Filter (CUF) on actual dissolved H-4 calcine and dissolved Run 1027 non-radioactive pilot plant calcine. The purpose of this testing was to evaluate the removal and operational efficiency of crossflow filtration on slurries of various solids loading. The solids loadings tested were, 0.19, 2.44 (H-4) and 7.94 (1027) weight percent, respectively. A matrix of test patterns was used to determine the effects of transmembrane pressure and axial velocity on filtrate flux. Filtrate flux rates for each solids loading displayed a high dependence on transmembrane pressure, indicating that pressure filtration resistance limits filtrate flux. Filtrate flux rates for all solids loading displayed a negative dependency on axial velocity. This would suggest axial velocities tested were efficient at removing filter cake.