The Eurex Process: Processing of Irradiated U-Al Alloys by Amine Solvent Extraction

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Abstract
The possibility of using long chain tertiary amines as extracting agents in the recovery and decontamination of uranium from irradiated U-Al alloys has been investigated. Nitric acid dissolution of MTR type fuel elements yields a solution with a high Al/U molar ratio. Due to the salting out action of aluminum nitrate, uranium is easily extracted from the aqueous phase by a suitable tertiary amine-diluent system; fission product nitrates are much less extractable and good decontamination factors are attainable. U partition coefficients and fission product decontamination factors are influenced by the concentration of nitric acid, aluminum nitrate, and uranyl nitrate; the effect of these variables is discussed. The chemical stability of the aminediluent system in the presence of nitric acid and nitrates is excellent in the experimental conditions of the process: the radiation stability has been examined under simulated process conditions: high exposure rates result in a decreased Zr decontamination without causing retention of U in the organic phase: a suitable solvent clean up, however, restores normal decontamination factors. The Eurex flowsheet is based on two separate extraction cycles: in both cycles the organic phase is 4 vol.% Alamind 336 in an aromatic hydrocarbon diluent. The salting out action in the second cycle is providee by adding aluminum nitrate to the scrub solution. The expected advantages of this new flowsheet are connected with the higher selectivity of the amine solvent which permits a higher decontamination factor and therefore a reduction of the number of extraction cycles. The resulting savings in equipment, ancillary and analytical services, and hot cell space will lower both capital and operating costs. Based on the Eurex flowsheet a small size plant will be constructed to process MTR type fuel assemblies.

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