Title: DISSOLUTION OF PLUTONIUM-BEARING RESIDUES IN A NITRIC ACID--CALCIUM FLUORIDE SOLVENT SYSTEM.

This research accomplished two goals. The first was to develop a computer program to simulate a cascade dissolver system. This program would be used to predict the bulk rate of dissolution in incinerator ash. The other goal was to verify the model in a single-stage dissolver system using Dy/sub 2/O/sub 3/. PuO/sub 2/ (and all of the species in the incinerator ash) was assumed to exist as spherical particles. A model was used to calculate the bulk rate of plutonium oxide dissolution using fluoride as a catalyst. Once the bulk rate of PuO/sub 2/ dissolution and the dissolution rate ofmore » all soluble species were calculated, mass and energy balances were written. A computer program simulating the cascade dissolver system was then developed. Tests were conducted on a single-stage dissolver. A simulated incinerator ash mixture was made and added to the dissolver. CaF/sub 2/ was added to the mixture as a catalyst. A 9M HNO/sub 3/ solution was pumped into the dissolver system. Samples of the dissolver effluent were analyzed for dissolved and F concentrations. The computer program proved satisfactory in predicting the F concentrations in the dissolver effluent. The experimental sparge air flow rate was predicted to within 5.5%. The experimental percentage of solids dissolved (51.34%) compared favorably to the percentage of incinerator ash dissolved (47%) in previous work. No general conclusions on model verification could be reached. 56 refs., 11 figs., 24 tabs.« less

Laboratory runs demonstrated successful dissolution of plutonium-bearing slag and crucible residues. The plutonium recovery was quantitative. Vigorous reaction during initial dissolution of each solids charge caused formation of large quantities of reaction foam. While the foam subsides in a few minutes, the foam volume could result in a boilover from the dissolver. Charging of smaller batches more frequently will minimize the problem. All the experimental runs exhibited the formation of a residual solids heel in the dissolver. Since heel dissolution is slow, periodic dissolver clean-out runs will be required to maintain a low heel volume. Any excessive solids heel buildupmore » can be removed and dissolved in a lengthy batch treatment using 4M HNO/sub 3/ or 6M HCl. The residne in a 32-hour continuous run was 8% by weight of the solids charged. It was determined that a 27.5 g/l iodate concentration was required in the dissolver overflow solution to precipitate plutonium iodate. The iodate concentration in the continuous dissolver is much less than this value (<5 g/l); therefore, formation of this inextractable precipitate should not be encountered. Dissolver overflow solution adjusted to solvent extraction feed composition was contacted with 20% TBP-80% CCl/sub 4/ (volume basis). Four stages of extraction reduced the plutonium concentration in the aqueous feed to 0.003 g/l. Storage of feed material for five days did not effect the plutonium extraction. The presence of up to 0.08M titanium or 0.3M sulfate did not decrease the extractability of the plutonium. (auth)« less