A ceramic waste form is being developed at Argonne National Laboratory forwaste generated during the electrometallurgical treatment of spent nuclearfuel. The waste is generated when fission products are removed from theelectrolyte, LiCI-KCl eutectic. The ceramic waste form is a composite,fabricated by hot isostatic pressing a mixture of glass frit and zeoliteoccluded with fission products and salt. Past work has shown that thenormalized release rate (NRR) is less than 1 g/m2d for allelements in a Material Characterization Center-Type 1 (MCC-1) leach test runfor 28 days in deionized water at 90°C (363 K). This leach resistance iscomparable to that of early Savannah River glasses. We are investigating howleach resistance is affected by changes in the cationic form of zeolite andin the glass composition. Composites were made with three forms of zeolite Aand six glasses. We used three-day ASTM C1220–92 (formerly MCC-1) leachtests to screen samples for development purposes only. The leach testresults show that the glass composites of zeolites 5A and 4A retain fissionproducts equally well. The loss of cesium is small, varying from 0.1 to 0.5wt%, while the loss of divalent and trivalent fission products is one ormore orders of magnitude smaller. Composites of 5A retain chloride ionbetter in these short-term screens than 4A and 3A. The more leach resistantcomposites were made with durable glasses that were rich in silica and poorin alkaline earth oxides. The x-ray diffraction (XRD) results show that asalt phase was absent in the leach resistant composites of 5A and the betterglasses but was present in the other composites with poorer leachperformance. Thus, the data show that the absence of a salt phase in acomposite's XRD pattern corresponds to improved leach resistance. The dataalso suggest that the interactions between the zeolite and glass depend onthe composition of both.