(331d) Effect of Salt and Zeolite Particle Size on Preparation of Salt-Loaded Zeolite in the Ceramic Waste Process

Electrorefining of spent nuclear fuel results in accumulation of fission products, actinides, and sodium in the molten LiCl-KCl electrolyte. To minimize effects on the process, salt must be periodically purified or disposed of. While advanced separations processes are being developed to enable purification of the salt, the current baseline process for treating spent EBR-II fuel at Idaho National Laboratory is based on the throw-away method. Contaminated salt is removed from either one of the two electrorefiners, crushed, milled, and blended using with dry zeolite-A using a high temperature v-mixer. The blending results in absorption of the salt into the zeolite pores. Glass frit is then mixed with the salt-loaded zeolite, and the mixture is heated to 925oC in the pressureless consolidation furnace. This technology was officially demonstrated for the U.S. Department of Energy in 1999 with small (1.5 kg) waste forms that contained Mark-IV electrorefiner salt after processing 100 driver sub-assemblies. More recently, efforts have been centered on procuring and installing new ceramic waste equipment, optimizing process parameters, and preparing for process qualification.

The focus of this paper is on optimizing process parameters for the ceramic waste process. In particular, particle size of the glass, zeolite, and salt is addressed. Initially, the process utilized zeolite and glass powders with particle sizes less than 10 ?Ým. Powder handling difficulties, however, dictated that larger particulate be used for both of these materials. After ceramic waste forms were successfully made via the pressureless consolidation method using 45-250 ?Ým zeolite, this was selected as the new nominal particle size range for both zeolite and glass. Salt particle size has never been well defined, since it is a product of in-cell milling. It is not possible to remove fine or coarse salt particles in the hot cell.

Due to the large size of the demonstration v-mixer and resulting high cost in operating it, a lab-scale unit was developed for out-of-cell experiments with non-radioactive surrogate salt. This unit has been used to test various v-mixer operating parameters°Xsuch as heating time, batch size, zeolite particle size, and salt particle size. After each test, samples of salt-loaded zeolite are taken and analyzed for surface salt. Also, the interior of the v-mixer is inspected for residual patches of salt and zeolite. It has been found that the presence of extremely fine salt particles leads to formation of these salt/zeolite patches on the inside of the v-mixer. For this paper, a systematic examination was made of the salt and zeolite particle sizes and will be reported.

Besides effectiveness of the salt/zeolite blending, material handling is also affected by material particle size. A useful instrument for assessing material handling properties is the Johannson Indicizer. Three different sets of indices related to powder handling, each measured using a different kind of indicizer, can be measured and used to design powder handling equipment. Recent results of indicizer measurements using zeolite, glass frit, and salt with reference particle sizes will be presented and discussed relative to the impact on salt processing.