Multiscale Speciation of U and Pu at Chernobyl, Hanford, Los Alamos, McGuire AFB, Mayak, and Rocky Flats

Abstract

The speciation of U and Pu in soil and concrete from Rocky Flats and in particles from soils from Chernobyl, Hanford, Los Alamos, and McGuire Air Force Base and bottom sediments from Mayak was determined by a combination of X-ray absorption fine structure (XAFS) spectroscopy and X-ray fluorescence (XRF) element maps. These experiments identify four types of speciation that sometimes may and other times do not exhibit an association with the source terms and histories of these samples: relatively well ordered PuO2+x and UO2+x that had equilibrated with O2 and H2O under both ambient conditions and in fires or explosions; instances of small, isolated particles of U as UO2+x, U3O8, and U(VI) species coexisting in close proximity after decades in the environment; alteration phases of uranyl with other elements including ones that would not have come from soils; and mononuclear Pu-O species and novel PuO2+x-type compounds incorporating additional elements that may have occurred because the Pu was exposed to extreme chemical conditions such as acidic solutions released directly into soil or concrete. Our results therefore directly demonstrate instances of novel complexity in the Å and μm-scale chemical speciation and reactivity of U and Pu in their initial formation and after environmental exposure as well as occasions of unexpected behavior in the reaction pathways over short geological but significant sociological times. They also show that incorporating the actual disposal and site conditions and resultant novel materials such as those reported here may be necessary to develop the most accurate predictive models for Pu and U in the environment.

The nature of Pu-bearing particles from the Maralinga nuclear testing site, Australia

“…The Maralinga particles are models for hot particles released during subcritical nuclear incidents, and are also useful in nuclear forensics as proxies for those generated from dirty bombs 8 . Overall, these new results corroborate that particle inhomogeneity and morphology 1 , 2 , 9 are as or even more important as the speciation as determinants of the fate of U and Pu in the environment, and demonstrate that the accuracy of predictive models depends on the inclusion of these parameters obtained from experimental measurements.…”

“…In particular, the distinctive texture of Potatohead (Fig. 3 a–c) is remarkably similar to that of the particles from Palomares 39 and Thule 40 ; and hot particles from the McGuire Air Force Base accident have µSXRF images and Pu–U correlations similar to either Bruce and Potatohead 9 . In summary, hot particles released via high energy sub-critical incidents acquire their compositions and textures at high temperature within the explosion cloud, and this mode of formation sets the scene for their long-term environmental behaviour 1 .…”

“…accidents where energy is released from external fires or conventional explosives. Since these tests, the world has documented a few instances of such incidents (Table S5 , SI-Previous studies ), including the B-52 accidents that resulted in the conventional detonation of thermonuclear weapons near Palomares, Spain 39 and Thule, Greenland 39 , 40 ; and the explosion of an armed nuclear missile and subsequent fire at the McGuire Air Force Base, USA 9 . Hot particles from these sub-critical nuclear incidents share the chemical and textural heterogeneity of the Maralinga particles as a result of the similar mode of formation from polymetallic melts.…”

Transformation of Ferrihydrite to Goethite and the Fate of Plutonium

“…These were fitted as 6(1) Pu-Fe scatterers at 3.17 43,[65][66][67][68][69] Lastly the EXAFS data are not inconsistent with the formation of a distinct poorly ordered Pu-Fe solid phase as has been hinted at in forensics literature, 56 although the formation of a distinct Pu-Fe phase was not supported by TEM imaging. Overall the TEM and EXAFS data demonstrate that PuO2 exists at the highest concentration Pu coprecipitation samples (3000 ppm) but not the lower concentrations (1000 and 400 ppm).…”

Speciation of Uranium and Plutonium From Nuclear Legacy Sites to the Environment: A Mini Review

“…Uranium can enter the environment in the form of uranium dioxide particles during an accidental discharge, such as the pollution of the Yenisei River (Bolsunovsky et al, 2017 ), and via regular technological influxes of liquid RW into storage pools, in which liquid RW accumulates in the bottom sediments and into sludge storage pools (Batuk et al, 2015 ).…”