Properties of carbonized and converted uranium-loaded weak-acid resins

Weak-acid ion-exchange resins have been found to provide a practical method for fabricating uranium-containing HTGR fuel kernels. Two steps, thermal decomposition or carbonization and carbothermic reduction of UO2 or conversion, are required in the manufacture of these kernels. The property variations during carbonization of uranium-loaded weak-acid resin-derived fuel proceeds in a manner closely analogous to its thermogravimetric characteristics, particularly the weight loss, volume loss, carbon-to-uranium ratio, density, and particle size. The heating rate through the critical portion of the thermogravimetric curve closely controls the resultant weight loss, volume loss, density, carbon-to-uranium ratio, and subsequent thermal behavior. The optimum carbonization cycle derived dictates a heating rate of 20C/min from 350 to 4400C, and the maximum practicable rate outside of this range. The conversion of the carbonized material is predictable from classical bulk thermodynamics for removal of carbon monoxide from UO2 + C. Relative phase compositions of UO2, UC2 and UC/sub 1-x/O/sub x/ can be controlled by adjusting conversion conditions. Agglomeration during conversion can be controlled by lowering the carbonization rate and/or conversion temperature and increasing gas flow. During this process Duolite C-464 resin appears more resistant to sticking than does Amberlite IRC-72