Influence of Oxidation States on Plutonium Mobility during Long-Term Transport through an Unsaturated Subsurface Environment

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• 作者：Daniel I. Kaplan ; Brian A. Powell ; Deniz I. Demirkanli ; Robert A. Fjeld ; Fred J. Molz ; Steven M. Serkiz ; and John T. Coates
• 刊名：Environmental Science & Technology
• 出版年：2004
• 出版时间：October 1, 2004
• 年：2004
• 卷：38
• 期：19
• 页码：5053 - 5058
• 全文大小：153K
• 年卷期：v.38,no.19(October 1, 2004)
• ISSN：1520-5851

文摘

Lysimeter and laboratory studies were conducted toidentify the controlling chemical processes influencingPu(IV) mobility through the vadose zone. A 52-L lysimetercontaining sediment from the Savannah River Site,South Carolina and solid Pu^IV(NO₃)₄ was left exposed tonatural wetting and drying cycles for 11 years before thelysimeter sediment was sampled. Pu had traveled 10cm, with >95% of the Pu remaining within 1.25 cm of thesource. Laboratory studies showed that the sedimentquickly reduced Pu(V) to Pu(IV) (the pseudo-first-orderreduction rate constant, k'_obs, was 0.11 h^-1). Of particularinterest was that this same sediment could be inducedto release very low concentrations of sorbed Pu underoxidizing conditions, presumably by oxidation of sorbed Pu(IV)to the more mobile Pu(V) species. Transport modelingsupported the postulation that Pu oxidation occurred inthe lysimeter sediment; the inclusion of an oxidation termin the model produced simulations that capture the Pudepth profile data. By not including the oxidation processin the model, Pu mobility was grossly underestimatedby a factor of 3.5. It is concluded that both oxidation andreduction mechanisms can play an important role in Putransport through the vadose zone and should be consideredwhen evaluating disposal of Pu-bearing wastes.