Dissolution cerium , plutonium

Complete dissolution of plutonium residues, especially high temperature calcined plutonium dioxide contained in residues such as incinerator ash, continues to cause problems, despite continued research since the Manhattan Project (9). Methods to improve the Rocky Flats system include the use of additives (e.g., cerium) and electrochemistry, other solvents (HCl-SnCl2) as well as high-temperature fusion methods (10). High pressure dissolution, HF preleaching, fluorination, and other methods are being investigated. 

Standard Practice for Preparation and Dissolution of Plutonium Materials for Analysis Standard Test Method for Plutonium by Iron (II)/Chromium (VI) Amperometric Titration Standard Test Method for Plutonium by Ti-tanium(III)/Cerium(IV) Titration Standard Test Method for Uranium by Iron (II) Reduction in Phosphoric Acid Followed by Chromium (VI) Titration in the Presence of Vanadium... 

In all cases, however, dissolution of irradiated fuel in nitric acid leaves some plutonium associated with undissolved fission products. This plutonium can be leached from the residue with mixed nitric and hydrofluoric acids or with mixed nitric acid and ceric nitrate, Ce(N03)4 [U2]. Residue from irradiated mixed UO2-PUO2 fuel was 99.94 percent dissolved in 4 h by treatment with 4 M HNO3-O.5 M Ce(IV). Ceric nitrate is preferred to HF in the secondary dissolution step because cerium is already present as a fission product, and its addition does not complicate subsequent solvent extraction. Use of Ce(IV) in the primary dissolution step is undesirable because it would convert all plutonium to the less extractive hexavalent state and would volatilize much of the ruthenium as RUO4. 

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