Generation and Characteristics of Plutonium and Americium Contaminated Soils Underlying Waste Sites at Hanford

Delegard, Calvin H.; Emerson, Hilary P.; Cantrell, Kirk J.; Pearce, Carolyn I.

doi:10.2172/1682309

Cited by 2 publications

(28 citation statements)

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“…17 However, Am was more mobile than Pu in sediments that reacted with acidic wastes than for neutral pH to alkaline wastes. 7 For example, Am/Pu ratios are relatively constant with depth in the neutral waste samples from Z-12 crib, indicating similar mobility of Am associated with Pu, whereas, in the acidic waste samples from below Z-9 trench, Am shows greater mobility based on the Am/Pu ratios.…”

Section: Introductionmentioning

confidence: 93%

“…The Z-12 crib wastes arose from waterjet scrubbing of hydrofluorinator off-gases, water scrubs of Pubearing scrap incinerator fumes, and dilute acid wastes, which were originally collected in a settling tank prior to discharge to the crib. 7 The Z-9 trench and Z-12 crib also received significantly different masses of Pu and Am, with an estimated 90 and 0.87 kg of Pu to Z-9 trench and Z-12 crib, respectively, and approximately 2.3 kg of 241 Am present in the waste initially disposed to the Z-9 trench, although estimates were not identified for Z-12 crib. The speciation of Pu and Am in these waste streams is not known to have been directly measured.…”

Section: Introductionmentioning

confidence: 97%

“…8,28 At the Hanford Site, 2.8 × 10 8 liters of process waste solutions containing Pu mixed with other contaminants were released into the subsurface during Pu finishing steps incurred for the weapons production mission from 1943 to 1990. 7 Pu and Am were released primarily as liquid process wastes but these wastes also contained Pu-bearing particulates. Some of the major ground disposal structures for Pu-bearing waste from Plutonium Finishing Plant (PFP) operations were the 216-Z-9 trench and the 216-Z-12 crib.…”

Section: Introductionmentioning

confidence: 99%

“…Some of the major ground disposal structures for Pu-bearing waste from Plutonium Finishing Plant (PFP) operations were the 216-Z-9 trench and the 216-Z-12 crib. The generation and characteristics of wastes disposed to these sites have been described by Delegard et al (2019). Briefly, the wastes were complex, containing varying amounts of cations (aluminum, calcium, iron, and sodium), anions (primarily nitrate and fluoride but also sulfate, chloride, and phosphate), and organic compounds (e.g., lard oil, TBP, and their degradation products), all of which may influence long-term Pu and Am mobility in the environment.…”

Section: Introductionmentioning

confidence: 99%

“…Briefly, the wastes were complex, containing varying amounts of cations (aluminum, calcium, iron, and sodium), anions (primarily nitrate and fluoride but also sulfate, chloride, and phosphate), and organic compounds (e.g., lard oil, TBP, and their degradation products), all of which may influence long-term Pu and Am mobility in the environment. 7 The Z-9 trench and Z-12 crib are two of several disposal sites that received markedly different waste streams. The Z-9 trench received smaller volumes (4.09 × 10 6 liters) of high ionic strength, low pH waste from 1955 to 1962, and the Z-12 crib received larger volumes (281 × 10 6 liters) of low ionic strength, neutral pH waste from 1959 to 1973.…”

Section: Introductionmentioning

confidence: 99%

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Influences on Subsurface Plutonium and Americium Migration

Emerson

Pearce

Delegard³

et al. 2021

ACS Earth Space Chem.

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Plutonium (Pu) has been released to the environment worldwide, including approximately 1.85 × 1015 Bq (200 kg) of Pu from process waste solutions to unconfined soil structures at the Hanford Site in Washington State. The subsurface mobility of Pu is influenced by complex interactions with sediments, groundwater, and any co-contaminants within the waste stream. Previous investigations at Hanford have shown that Pu exists as discrete PuO2 particles forming before or after disposal, as secondary solid phases formed from waste interactions with sediments as adsorbed/incorporated species, and/or as dissolved species. In this research, new evidence is presented for the existence of PuO2, PuO2-Bi2O3 composites, and particles from burnt Pu metal in near-surface sediments where Pu-laden acidic process waste was disposed to sediments. Pu and americium (Am) L 3 X-ray absorption spectroscopy and density functional theory suggest that, in larger, more crystalline PuO2 particles, Am formed from radioactive decay is retained in the PuIVO2 structure as AmIV. The Pu and Am that were disposed of in an acidic waste stream have since migrated deeper into the subsurface with detection to at least 37 meters below ground surface. In contrast, Pu deposited near the ground surface from neutral pH waste is found to be homogeneously distributed and relatively immobile. Groundwater extractions performed on contaminated sediments indicate that both Pu and Am are recalcitrant, with Am being fractionally less extractable than Pu on a molar basis. These results suggest that the more mobile fraction of Am has migrated from the near-surface and may be present in the deeper sediments as a different phase than Pu. From these results, it is suggested that Pu and Am deposited from acidic wastes were initially mobile and became significantly less mobile as wastes were neutralized within the soil profile.

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Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influences on Subsurface Plutonium and Americium Migration

Emerson

Pearce

Delegard³

et al. 2021

ACS Earth Space Chem.

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Subsurface Transport of Plutonium in Organic and Aqueous Acidic Processing Wastes at the Hanford Site, USA

Baumer,

Zavarin,

Pearce

et al. 2024

Environ. Sci. Technol.

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Over 4 million liters of mixed acidic (∼pH 2.5), high ionic strength (∼5 M nitrate) plutonium (Pu) processing waste were released into the 216-Z-9 (Z-9) trench at the Hanford Site, USA, and trace Pu has migrated 37 m below the trench. In this study, we used flowthrough columns to investigate Pu transport in simplified processing waste through uncontaminated Hanford sediments to determine the conditions that led to Pu migration. In low pH aqueous fluids, some Pu breakthrough is observed at pH < 4, and increased Pu transport (14% total Pu breakthrough) is observed at pH < 2. However, Pu migrates in organic processing solvents through low pH sediments virtually uninhibited with approximately 94 and 86% total Pu breakthrough observed at pH 1 and pH 3, respectively. This study demonstrates that Pu migration can occur both with and without organic solvents at pH < 4, but significantly more Pu can be transported when partitioned into organic processing solvents. Our data suggest that under acidic conditions (pH < 4) in the vadose zone beneath the Z-9 trench, Pu present in organic processing solvents moved relatively unhindered and may explain the historical downward migration of Pu tens of meters below the Z-9 trench.

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Generation and Characteristics of Plutonium and Americium Contaminated Soils Underlying Waste Sites at Hanford

Cited by 2 publications

References 0 publications

Influences on Subsurface Plutonium and Americium Migration

Influences on Subsurface Plutonium and Americium Migration

Subsurface Transport of Plutonium in Organic and Aqueous Acidic Processing Wastes at the Hanford Site, USA

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