Dissolution of PuO$sub 2$ with cerium(IV) and fluoride promoters

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Ce(IV) in low concentrations is an effective promoter of PuO$sub 2$ dissolution in nitric acid solutions of approximately 3 to 6M. However, stoichiometric quantities of Ce(IV) are required for complete dissolution, and hydrothermal precipitation of CeO$sub 2$ is a potential problem at low acidities. Dissolution proceeds with oxidation of Pu(IV) to Pu(VI) with a corresponding reduction of Ce(IV). When an excess of Ce(IV) is present, the dissolution rate depends on Ce(IV) concentration below approximately 0.1M Ce(IV); above this concentration, the rate becomes fairly constant. Increased PuO$sub 2$ sintering temperature markedly reduces the dissolution rate in 4M HNO$sub 3$-0.15M Ce(IV). Preliminary ... continued below

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Pages: 31

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Harmon, H.D. October 1, 1975.

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  • Savannah River Laboratory
    Publisher Info: Du Pont de Nemours (E.I.) and Co., Aiken, S.C. (USA). Savannah River Lab.
    Place of Publication: Aiken, South Carolina

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Ce(IV) in low concentrations is an effective promoter of PuO$sub 2$ dissolution in nitric acid solutions of approximately 3 to 6M. However, stoichiometric quantities of Ce(IV) are required for complete dissolution, and hydrothermal precipitation of CeO$sub 2$ is a potential problem at low acidities. Dissolution proceeds with oxidation of Pu(IV) to Pu(VI) with a corresponding reduction of Ce(IV). When an excess of Ce(IV) is present, the dissolution rate depends on Ce(IV) concentration below approximately 0.1M Ce(IV); above this concentration, the rate becomes fairly constant. Increased PuO$sub 2$ sintering temperature markedly reduces the dissolution rate in 4M HNO$sub 3$-0.15M Ce(IV). Preliminary results indicate stainless steel corrosion rates in Ce(IV)-HNO$sub 3$ solutions increase to significant values with increasing Ce(IV) concentration. In HNO$sub 3$-KF, the PuO$sub 2$ dissolution rate increases rapidly as the nitric acid and fluoride concentrations increase. The rate is decreased by increased PuO$sub 2$ sintering temperature and the presence of cationic species such as UO$sub 2$$sup 2+$ and Fe$sup 3+$, which complex fluoride. Dissolution is much more rapid in HNO$sub 3$-KF solutions than in HNO$sub 3$-Ce(IV). Mixed KF and Ce(IV) in certain mole ratios in 8M HNO$sub 3$ gives more rapid dissolution than with Ce(IV) or KF alone; more Ce(IV) retards dissolution. In HNO$sub 3$-0.05M Ce(IV)--0.1M KF, the dissolution rate increases as HNO$sub 3$ concentration increases; below 6M HNO$sub 3$, the mixed system containing 0.05M Ce(IV)-0.1M KF is less effective than HNO$sub 3$-Ce(IV) or HNO$sub 3$-KF. Ruthenium, present in irradiated PuO$sub 2$, catalytically reduces Ce(IV) in nitric acid; thus, Ce(IV) will be ineffective for irradiated PuO$sub 2$-UO$sub 2$ fuel. In view of the ruthenium problem, HNO$sub 3$-F$sup -$ solutions appear most promising for breeder fuel processing. Nitric acid solutions containing Ce(IV) and Ce(IV)- F$sup -$ mixtures may be most useful for dissolving unirradiated PuO$sub 2$ and UO$sub 2$-PuO$sub 2$ materials, as in scrap recovery operations. (auth)

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Pages: 31

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Dep. NTIS

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  • Other Information: Orig. Receipt Date: 30-JUN-76

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  • Report No.: DP--1371
  • Grant Number: AT(07-2)-1
  • Office of Scientific & Technical Information Report Number: 4165991
  • Archival Resource Key: ark:/67531/metadc865793

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  • October 1, 1975

Added to The UNT Digital Library

  • Sept. 16, 2016, 12:32 a.m.

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  • Feb. 17, 2017, 3:04 p.m.

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Harmon, H.D. Dissolution of PuO$sub 2$ with cerium(IV) and fluoride promoters, report, October 1, 1975; Aiken, South Carolina. (digital.library.unt.edu/ark:/67531/metadc865793/: accessed October 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.