Eleven-Year Field Study of Pu Migration from Pu III, IV, and VI Sources

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• 作者：Daniel I. Kaplan ; Deniz I. Demirkanli ; Leo Gumapas ; Brian A. Powell ; Robert A. Fjeld ; Fred J. Molz ; and Steven M. Serkiz
• 刊名：Environmental Science & Technology
• 出版年：2006
• 出版时间：January 15, 2006
• 年：2006
• 卷：40
• 期：2
• 页码：443 - 448
• 全文大小：328K
• 年卷期：v.40,no.2(January 15, 2006)
• ISSN：1520-5851

文摘

Understanding the processes controlling Pu mobility inthe subsurface environment is important for estimating theamount of Pu waste that can be safely disposed invadose zone burial sites. To study long-term Pu mobility,four 52-L lysimeters filled with sediment collected from theSavannah River Site near Aiken, South Carolina wereamended with well-characterized solid Pu sources (Pu^IIICl₃,Pu^IV(NO₃)₄, Pu^IV(C₂O₄)₂, and Pu^VIO₂(NO₃)₂) and left exposedto natural precipitation for 2-11 years. Pu oxidationstate distribution in the Pu(III) and Pu(IV) lysimeterssediments (a red clayey sediment, pH = 6.3) were similar,consisting of 0% Pu(III), >92% Pu(IV), 1% Pu(V), 1%Pu(VI), and the remainder was a Pu polymer. These threelysimeters also had near identical sediment Pu concentrationprofiles, where >95% of the Pu remained within 1.25 cm ofthe source after 11 years; the other 5% of Pu moved atan overall rate of 0.9 cm yr^-1. As expected, Pu moved morerapidly through the Pu(VI) lysimeter, at an overall rate of12.5 cm yr^-1. Solute transport modeling of the sediment Puconcentration profile data in the Pu(VI) lysimeter indicatedthat some transformation of Pu into a much less mobileform, presumably Pu(IV), had occurred during the courseof the two-year study. This modeling also supported previouslaboratory measurements showing that Pu(V) or Pu(VI)reduction was 5 orders of magnitude faster than correspondingPu(III) or Pu(IV) oxidation. The slow oxidation rate (1 ×10^-8 hr^-1; t_1/2 = 8000 yr) was not discernible from the Pu(VI)lysimeter data that reflected only two years of transportbut was readily discernible from the Pu(III) and Pu(IV) lysimeterdata that reflected 11 years of transport.