The long-time (>100 h of operation) flux was measured for a set of five tests where nuclear waste slurry simulant was separated and continuously recycled using a stainless steel cross-flow filter. The tests were conducted at various constant axial velocities and transmembrane pressures. In all five tests, the filter flux continued to decay at long times and did not reach a steady-state value. The long-time slope of the flux decay was unaffected by the axial velocity, but a larger transmembrane pressure resulted in a larger slope. Post-test examination of the filter did not show evidence of significant depth fouling. The experimental results are compared to theoretical predictions of the time to initiate cake formation and the time to reach steady-state predicted by models from the literature, both of which do not imply long-time phenomena would be expected. A more reasonable match between theory and experiment was achieved using a model based on the principles of dead-end filtration. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.