Sources and Migration of Plutonium in Groundwater at the Savannah River Site

Dai, Minhan; Kelley, James M.; Buesseler, Ken O.

doi:10.1021/es020025t

Cited by 106 publications

(139 citation statements)

References 27 publications

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“…Pu isotopes were analyzed using a three-stage TIMS instrument at the Pacific North National Lab (PNNL) (Dai et al, 2002 and references therein). For sample sizes where millions of ion counts are measured using internal standards to correct for isotopic fractionation, the TIMS instrument is capable of measuring these ratios to 1 part per thousand precision and accuracy.…”

Section: Discussionmentioning

confidence: 99%

“…More recent review of these data suggests that Pu detected in downstream wells could not have entered through groundwater and thus the potential for Pu migration via colloidal transport may have been overstated (Marty et al,3 1997). Our own data from the Savannah River Site (SRS), suggest that groundwater Pu is predominantly in more oxidized forms and not associated with colloids (Dai et al, 2002).…”

Section: Introductionmentioning

confidence: 94%

“…At this location, unfiltered samples were taken from wells K-11 and K-109A for total Pu isotopic composition analysis. In addition, 4 sites were sampled in greater detail (wells K-27, 32A, K-36, and K-110A) using our combination of low flow rate well sampling, cross-flow ultrafiltration (CFF), redox speciation and thermal ionization mass spectrometry (TIMS) techniques, detailed procedures of which have been described elsewhere (Dai et al, 2002). A water sample was also taken from the Columbia River downstream of the 100K-Area.…”

Section: Well Samplingmentioning

confidence: 99%

“…Our CFF system retained >91 % of a ~3 kDa dextran carbohydrate colloid and >94% of a 14.5 kDa protein standard. As we have noted (Dai et al, 2002), identical CFF membranes from the same manufacturer can have varying retention properties; thus, calibration of each CFF membrane is mandatory.…”

Section: On Site Cff and Redox Processingmentioning

confidence: 99%

“…Redox processing consisted of separating the plutonium in the aliquots into Pu(III/IV) and Pu(V/VI) subfractions by a method presented in detail in Dai et al (2002) which was adapted from Lovett and Nelson (Lovett and Nelson, 1981).…”

Section: On Site Cff and Redox Processingmentioning

confidence: 99%

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Plutonium in groundwater at the 100K-Area of the U.S. DOE Hanford Site

Dai

Buesseler

Pike

2005

Journal of Contaminant Hydrology

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We examined the concentration, size distribution, redox state and isotopic composition of plutonium (Pu) in groundwater at the 100K-Area at the US Department of Energy's (DOE) Hanford Site. Total concentrations of Pu isotopes were extremely low (10 -4 to 10 -6 pCi/kg, ≈ 10 4 to 10 6 atoms/kg), but measurable for the first time in the 100K-Area wells using mass spectrometric analyses that are much more sensitive than alpha spectroscopy methods used previously. Size fractionation data from two wells suggests that 7-29% of the Pu is associated with colloids, operationally defined here as particles between 1 kDa -0.2 µm in size. These colloids were collected using a 1 kDa cross-flow ultrafiltration system developed specifically for groundwater actinide studies to include careful controls both in the field and during processing to ensure in-situ geochemical conditions are maintained and size separations can be well characterized. Pu in this colloidal fraction was exclusively in the more reduced Pu(III/IV) form, consistent with the higher affinity of Pu for particle surfaces in the lower oxidation states. While the overall concentrations of Pu were low, the Pu isotopic composition suggests at least two local sources of groundwater Pu, namely local Hanford reactor operations at the 100K-Area, and spent nuclear fuel from the N reactor, which was stored in concrete pools at this site.Differences between this site and the Savannah River Site (SRS) are noted, since groundwater Pu at the F-Area seepage basin at SRS has been found using these same 2 methods, to be characterized by much lower colloidal abundances and higher oxidation states. This difference is not directly attributable to groundwater redox potential or geochemical conditions, but rather the physical-chemical difference in Pu sources, which at SRS appear to be dominated downstream from the seepage basins by decay of 244 Cm, resulting in more oxidized forms of 240 Pu. There is no clear evidence for colloid facilitated transport of Pu in groundwater at this site, since downstream wells have both an order of magnitude lower concentrations of Pu, but also a lower fractional colloidal distribution.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 94%

Section: Well Samplingmentioning

confidence: 99%

Section: On Site Cff and Redox Processingmentioning

confidence: 99%

Section: On Site Cff and Redox Processingmentioning

confidence: 99%

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Plutonium in groundwater at the 100K-Area of the U.S. DOE Hanford Site

Dai

Buesseler

Pike

2005

Journal of Contaminant Hydrology

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Plutonium: Radionuclides

Neu¹,

Goff²,

Runde³

2005

Encyclopedia of Inorganic Chemistry

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Plutonium is the most debated actinide element because of its dual use in devastating nuclear weapons and beneficial generation of nuclear energy. Plutonium metal exists in several allotropic phases and plutonium in solution exhibits a rich and complex chemistry. The ability to exist in up to four oxidation states makes plutonium unique among all elements. Pu(III) and Pu(VI) form only under reducing or oxidizing conditions, respectively; whereas Pu(IV) and Pu(V) have broad stability ranges within the geochemical bounds of environmental systems. When Pu(IV) is above trace concentration and particulate matter is present, then solids or suspended colloids are the predominant chemical forms. In contrast, Pu(V), as PuO $_{2}^{+}$ , has relatively higher solubility as an aquo species or a monomeric complex of natural ligands (hydroxide, chloride, sulfate, etc.). Stronger complexing, polydentate ligands, such as carbonate and organics, tend to increase plutonium solubility by forming very stable Pu(IV) complexes. Minerals, high molecular weight organic matter, and bacteria can either increase or decrease the solubility of plutonium, depending upon their chemical properties, mechanisms of interaction, and the geochemical conditions of the surrounding environment. Plutonium generally has very low solubility, low mobility, and few health consequences from environmental forms, and therefore poses little risk to living systems under nearly all conditions. This article provides a brief overview of the chemistry and behavior of plutonium in aqueous solutions and in the environment.

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