Initial evaluation of a hot isostatic pressed waste form from iodine-loaded silver-exchanged mordenite - 5225

Silver-exchanged mordenite (AgZ) is currently under evaluation for the capture of iodine from the off-gas streams that are expected to arise during the reprocessing of used nuclear fuel. The purpose of this study was to determine if hot isostatic pressing (HIPing) could directly convert iodine-loaded silver-exchanged mordenite (I-Ag⁰Z) into a suitable waste form. In this paper, we will examine the effects of pressing conditions (temperature and pressure), media composition (sodium mordenite vs. AgZ), and the ratio of iodine to mordenite on the characteristics of the resulting waste form. Iodine-containing mineral phases in the waste forms will be identified with x-ray diffraction, and surface characteristics will be examined with SEM/EDS. Although the resulting pellets did have an increase in density of 170% over the starting material, the samples were not found to be durable when subjected to a crush test. The use of HIPing was suggested as a way to produce a waste form with increased robustness. It was shown that, under the conditions used for pressing, the majority of the material transforms into an amorphous structure. The only crystalline phase observed in the pressed Ag⁰Z material was SiO₂. For the samples loaded with iodine (I-Ag⁰Z), iodine was present as AgI clusters at low temperatures and transformed into AgIO₄ at high temperatures