Coated particles made from ion exchange resins offer an attractive alternative to "fissile" particles specified for advanced HTGR's. The concept of reacting cation exchange resins in the hydrogen form with U03, using dilute uranyl salt solutions as a transfer mediun, has important advantages for preparation of HTGR fuel particles from ion exchange resins. Dowex 50W-X8 (with nuclear sulfuric acid exchange groups attached to a styrene-divinylbenzene "polymer lattice) satisfies the product requirements better than do other strong acid resins, but the sulfuric acid exchange group leaves sulfur in the carbonized particle. Weakly acidic cation exchange resins with carboxylic acid exchange groups leave only carbon and oxygen after carbonization and thus give particles more comparable with the UC_ or UO- commonly used for HTGR fuels. Amberlite IRC-72 was identified as having a better combination of properties than any other weak acid resin tested. The procedure of reacting UO, with cation exchange resins in the hydrogen form using uranyl nitrate as the transfer solution allows efficient and well controlled loading of either strong or weak acid resins without formation of dilute uranium solution. The , final solution concentration can be selected and controlled by mixing the desired amounts of UO,, resin, and solution without any need to monitor flow rates or concentrations. Mixing of UO, with the resin is the only procedure which has demonstrated practical, stoichiometric loadings of a weak acid resin with uranium. Satisfactory mixing of resins, UO,, and uranyl nitrate solution was demonstrated in agitated baffled vessels, in a screen-bottom basket of the resin-in pulp type of contactor, and in a fluidized resin bed with a separate mixer for the addition of UO,
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