Final published version
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
}
TY - JOUR
T1 - Influences on Subsurface Plutonium and Americium Migration
AU - Emerson, H.P.
AU - Pearce, C.I.
AU - Delegard, C.H.
AU - Cantrell, K.J.
AU - Snyder, M.M.V.
AU - Thomas, M.-L.
AU - Gartman, B.N.
AU - Miller, M.D.
AU - Resch, C.T.
AU - Heald, S.M.
AU - Plymale, A.E.
AU - Reilly, D.D.
AU - Saslow, S.A.
AU - Neilson, W.
AU - Murphy, S.
AU - Zavarin, M.
AU - Kersting, A.B.
AU - Freedman, V.L.
PY - 2021/2/18
Y1 - 2021/2/18
N2 - 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) L3 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. ©
AB - 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) L3 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. ©
KW - americium
KW - autoradiography
KW - fate and transport
KW - Hanford Site
KW - plutonium
KW - X-ray absorption spectroscopy
U2 - 10.1021/acsearthspacechem.0c00277
DO - 10.1021/acsearthspacechem.0c00277
M3 - Journal article
VL - 5
SP - 279
EP - 294
JO - ACS Earth and Space Chemistry
JF - ACS Earth and Space Chemistry
IS - 2
ER -