Low-level Radioactive-waste Site Research Articles

Rare earth elements and yttrium as tracers of waste/rock-groundwater interactions

Increasing concentrations of Rare Earth Elements (REE) plus yttrium (REY) are entering the environment due to human activities. The similar chemical behaviour across the whole REY, i.e. the lanthanide series (lanthanum to lutetium) and yttrium, allows their use as tracers, fingerprinting rock-forming processes and fluid-rock interactions in earth science systems. However, their use in fingerprinting waste and particularly low-level radioactive waste has not received much attention, despite the direct use of REE in the nuclear industry and the traditional use of REE as proxies to understand the environmental mobility of the actinide series (actinium to lawrencium). The highly instrumented low-level radioactive waste site at Little Forest (Australia) allows a detailed REY study, investigating interactions with local strata, neighbouring waste forms and shallow groundwater flows. Groundwater samples and solids from cored materials were recovered from 2007 to 2012 from the study site and regional baseline sites in the same geological materials. The REY in water samples were analysed by automated chelation pre-concentration (SeaFast, ESI) followed by ICP-MS determination, while solid samples were analysed using Neutron Activation Analysis (NAA) and X-ray fluorescence scanning (ITRAX). Solid rocks showed no REY departed from typical Upper Crust compositions in either Little Forest or regional background sites. Shallow groundwater from ~4–5 m, at or slightly below waste trench levels, showed water-waste interaction as a marked enrichment, relative to shale-normalised patterns, in samarium, europium and gadolinium, with depleted yttrium. Leachate samples from the neighbouring urban landfill show different REY normalised patterns. REY distribution changes with depth through increased interaction with shales and sandstones. Variations in pH and redox conditions lead to widespread precipitation of Fe-hydroxides, which scavenge REY with differential uptake by precipitating solids, resulting in increases in Y and higher Y/Ho ratio in the groundwater along the flow path. Our study revealed that the Little Forest low-level radioactive waste has a REY fingerprint different to that of groundwater in surrounding land uses. REY can be used to fingerprint diverse waste sources, assess the mobility of lanthanides inferring the mobility of selected actinides, and to trace the fate of REY during groundwater recharge. The approach presented can refine source allocation and trace pollutant mobility in current and legacy urban, mixed and radioactive waste sites around the world.

Emerging and Historical Contaminants Detected in Desert Rodents Collected Near a Low-Level Radioactive Waste Site.

In an effort to determine contaminant presence, concentrations, and movement from a low-level radioactive waste (LLRW) burial disposal site to ecosystems in the surrounding area, a study was developed to assess concentrations of per- and polyfluoroalkyl substances (PFAS), polychlorinated biphenyls (PCBs), and tritium. To complete this assessment small mammals, vegetation, soil, and insect samples were collected from areas within and adjacent to the Beatty, Nevada, LLRW site and from a reference area located approximately 3 km south of the LLRW site. Samples underwent analysis via liquid chromatography tandem mass spectrometry, gas chromatography mass spectrometry, or scintillation spectroscopy depending on the analyte of interest. Small mammal tissues showed maximum concentrations of over 1700 ng/g for PFAS, 1600 ng/g for PCBs, and 10 000 Bq/kg for tritium. The primary contaminants found in soil samples were PCBs, with maximum concentrations exceeding 25 ng/g. Trace amounts of PFAS were also detected in soils and insects. Only qualitative data were obtained from vegetation samples because of the complex matrix of the dominant plant species (creosote bush; Larrea tridentata [Sessé & Moc. ex DC.] Coville). Overall, these data indicate the presence of various anthropogenic contaminants in the ecosystem surrounding the LLRW area, but additional analyses are necessary to confirm the sources and migration pathways of PFAS and PCBs in this hyperarid environment. Environ Toxicol Chem 2021;40:727-734. © 2020 SETAC.

Identification of sources and processes in a low-level radioactive waste site adjacent to landfills: groundwater hydrogeochemistry and isotopes

Multiple tracer-element and isotope approaches were applied at a 1960s-era low-level radioactive waste burial site located in the Lucas Heights area on the southwest urban fringe of Sydney, Australia. The site is situated among other municipal and industrial (solid and liquid) waste disposal sites causing potential mixing of leachates. Local rainfall contains marine-derived major ion ratios that are modified during infiltration depending on waste interactions. The local geology favours the retention of contaminants by ion-exchange processes within the clay-rich soils and the shale layer underlying the burial site. Local soils experience periodic infiltration and wetting fronts that can fully saturate the waste trenches (bathtub effect) while surrounding soils are mostly unsaturated with discontinuous perched lenses. Within the trenches, the degradation of organic matter results in localised methanogenesis, as suggested by enriched δ2H and δ13CDIC values in adjacent subsurface water. Movement of contaminants from the trenches is indicated by Na+, Br− and I− concentrations, variations in 87Sr/86Sr, enriched δ13CDIC values and evolution of δ34S of dissolved sulfate in perched water bodies above the shale. Although transport is limited by the low transmissivity of the clay-rich soils, migration and mixing processes are indicated by the variation of concentrations with distance from the trenches, disappearance of δ2H enrichments, mixing with other sources of Sr and sulfate isotope fractionations. The depth distribution of waste-derived contaminants (specifically 3H and Be) between the perched water surrounding the trenches, and the underlying shale and sandstone layers, indicates limited downward transport of contaminants. Past removal of the shale layer in an adjacent site, Harrington's Quarry, has facilitated the mixing of some municipal waste leachates (characterised by circum-neutral pH, high alkalinity, low sulfate, high 3H, high Be, enriched δ2H and δ13CDIC) into the underlying groundwater system as suggested by high TDS, Cl−/Br− ratios, Be and 3H found in deeper wells. This study demonstrates the applicability of using trace elements, stable- and radio-isotopes to document the existing geochemistry and the contaminant transport from the waste trenches. The multiple tracer approach addresses the complexities of transport at the site and differentiates various municipal, industrial and radioactive waste sources.

Critical Mechanisms for Critical Masses: Exploring Variation in Opposition to Low-Level Radioactive Waste Site Proposals

Between 1986 and 1993, local activists in the U.S. organized more than 900 collective acts of public opposition to low-level radioactive waste site proposals across twenty-one counties. Yet, the number of such acts varied significantly across the counties. Both waste-siting professionals and social movement scholars have sought to identify factors of mobilization to explain such variation. An analysis of these cases reveals that a focus limited to pre-existing factors of mobilization—whether the demographic and economic factors favored by siting professionals, or the mobilization and political opportunity structures of the "classic social movement agenda"—badly misjudges mobilization. A paired comparison of two counties that differed dramatically in the number of acts of collective opposition mustered over the course of the siting process demonstrates the importance of social mechanisms that shape just how a community interacts with its political resources. The key differences between the two counties lie in the setting, sequence, and in the combination of the following social mechanisms: social appropriation, identify shift, and the attribution of threat and opportunity. To understand the assertion of local political power in an implementation process such as siting efforts, we need to understand not only the political resources available in a community context, but also the way in which human relationships shape the perception and application of that context.

Mineralogy of selected geological deposits from the United Kingdom and the Republic of Ireland as possible capping material for low-level radioactive waste disposal facilities

Solid low-level radioactive waste (LLW) is currently being disposed at a number of facilities in the United Kingdom (UK). The safety of these facilities relies to some extent on the use of engineered barriers, such as a cap and a liner, to isolate the waste and protect the environment. Generally, the material used as the barrier layer within such a cap should be of low permeability and it should retain this property over long timescales (beyond a few decades normally required for facilities containing non-radioactive wastes). The objective of this research is to determine the mineralogy of selected geological deposits from the UK and Republic of Ireland as part of a larger project to examine their suitability as a capping material, particularly on LLW sites. Mineral transformations, from weathering, may impact on the long-term performance of the cap and even the disposal facility. These transformations could be brought on or enhanced by climate change. X-ray diffraction (XRD) was carried-out on the sand, silt and clay fractions of the London Clay, Belfast Upper Boulder Clay, Irish Glacial Till, Belfast Sleech, and Ampthill Clay geological deposits. Minerals were present that could pose both positive and negative effects on the long-term performance of the cap. Smectite, which has a high shrink swell potential, may produce cracks in London Clay, Belfast Upper Boulder Clay and Ampthill Clay capping material during dry, hotter periods as a possible consequence of future climate change; thus, resulting in higher permeability. Ampthill Clay and Belfast Sleech had elevated amounts of organic matter (OM) at 5.93% and 5.88%, respectively, which may also contribute to cracking. Over time, this OM may decompose and result in increased permeability. Gypsum [CaSO 4] in the silt and sand fractions of Ampthill Clay may reduce the impact of erosion during wetter periods if it is incorporated into the upper portion of the cap. There are potential negative effects from the acidity created by the weathering of pyrite [FeS 2] present in the silt and sand fractions of Belfast Sleech and Ampthill Clay that could impede the growth of grasses used to stabilize the surface of the capping material if this material is used as part of the vegetative soil layer. Additionally, acidic waters generated from pyrite weathering could negatively impact the lower lying capping material and the disposal facility in general, because they could react with contaminants and weaken vessels storing contaminants. However, calcium carbonate [CaCO 3] present in the silt and sand fractions of these deposits, and dolomite [CaMg(CO 3) 2] in Belfast Sleech, may counter act the acidity.

Fe(III) Reduction in the Subsurface at a Low-level Radioactive Waste Disposal Site

The low-level radioactive waste (LLW) repository located near to the village of Drigg, Cumbria is the principal site for disposal of LLW in the United Kingdom. To gain a better understanding of the potential microbial processes that could control radionuclide mobility in the LLW repository, we studied of a range of anaerobic processes in microcosms constructed from sediments at the site. Sediment samples taken from both former disposal trenches and the far-field region of the site were analyzed for the presence of Fe(II) and bioavailable Fe(III) using chemical extractions and assays. Near-field (trench) sediments were found to have undergone some microbial reduction of iron, with acid-extractable Fe(II) present and 16S rRNA genes affiliated to known Fe(III)-reducing microorganisms detected in clone libraries constructed by PCR using broad-specificity primers. In far-field material, no Fe(II) was detectable although poorly crystalline Fe(III) was present. No 16S rRNA genes affiliated with known Fe(III)-reducing microorganisms were observed in clone libraries prepared with broad-specificity primers, suggesting that they were not numerically dominant in the far-field sediments. Time-course microcosm experiments were set up by amending the near- and far-field material with 10 mM acetate. The utilization of nitrate, poorly crystalline Fe(III) and sulfate was monitored to identify the sequence of terminal electron accepting processes in the sediments. Analysis of the microbial community after Fe(III) reduction had terminated revealed a large increase in 16S rRNA gene sequences affiliated to known Fe(III)-reducing bacteria, with a close relative to Ferribacterium limneticum accounting for 55% of the community. 16S rRNA analysis of the sediments post-Fe(III) reduction revealed the presence of some Fe(III)-reducing microorganisms such as a close relative of Rhodoferax ferrireducens. Nitrate, iron and sulfate data were then modeled with a biogeochemical reactive transport computer model that includes representation of microbial growth kinetics, and which is used to simulate the evolution of the subsurface geochemistry at the repository site. The potential impact of these processes on radionuclide mobility at LLW sites is discussed.

Disruption or Convention? A Process-based Explanation of Divergent Repertoires of Contention Among Opponents to Low-level Radioactive Waste Disposal Sites

Violence, disruption and convention constitute three well established categories of collective action repertoires available to contemporary social movements. What factors shape differences in repertoire selection across social movement groups? I take a process-based approach to answer this question, examining two grassroots opposition movements to the disposal of low-level radioactive waste in the United States. The two rural New York State counties I consider each faced a state-imposed low-level radioactive waste site proposal in 1988. Activists in each county mounted vigorous collective opposition to the proposed facility, while exhibiting distinct repertoires of collective action. Activists in Allegany County pursued disruptive civil disobedience, while activists in Cortland County pursued a conventional repertoire of citizen lobbying and litigation efforts. Similarities across a variety of demographic, political, and social characteristics in these two counties leave the standard explanations for repertoire selection put forth in the social movement literature wanting. I argue that the relationship developed between the respective county governments and citizen activists during the waste-site proposal dispute had a dramatic effect on the dominant repertoire of collective action adopted by each community. More specifically, identifying the presence or absence of the social mechanism of brokerage between local government and activists is crucial to understanding the different trajectories of these movement groups. This article highlights the utility of fine-grained process-based analysis as a complement to variable-based approaches for explaining social movement activity, and the importance of the mechanism of brokerage among local government and activists for understanding bottom-up movements responding to proximate grievances, such as the environmental justice movement.

Bioreduction of Uranium:  Environmental Implications of a Pentavalent Intermediate

The release of uranium and other transuranics into the environment, and their subsequent mobility, are subjects of intense public concern. Uranium dominates the inventory of most medium- and low-level radioactive waste sites and under oxic conditions is highly mobile as U(VI), the soluble uranyl dioxocation (UO2)2+. Specialist anaerobic bacteria are, however, able to reduce U(VI)to insoluble U(IV), offering a strategy for the bioremediation of uranium-contaminated groundwater and a potential mechanism for the biodeposition of uranium ores. Despite the environmental importance of U(VI) bioreduction, there is little information on the mechanism of this transformation. In the course of this study we used X-ray absorption spectroscopy (XAS) to show that the subsurface metal-reducing bacterium Geobacter sulfurreducens reduces U(VI) by a one-electron reduction, forming an unstable (UO2)+ species. The final, insoluble U(IV) product could be formed either through further reduction of U(V) or through its disproportionation. When G. sulfurreducens was challenged with the chemically analogous (NpO2)+, which is stable with respect to disproportionation, it was not reduced, suggesting that it is disproportionation of U(V) which leads to the U(IV) product. This surprising discrimination between U and Np illustrates the need for mechanistic understanding and care in devising in situ bioremediation strategies for complex wastes containing other redox-active actinides, including plutonium.

Near-field/Far-field Interface of a Near-Surface Low-Level Radioactive Waste Site

ABSTRACTExperimental and Modelling studies have been used to investigate the biogeochemical processes occurring at the interface zone between the near-field and far-field of the Drigg Low-Level radioactive Waste (LLW) trenches. These have led to a conceptual model of interface biogeochemistry, which has subsequently been modelled by the BNFL code known as the Generalised Repository Model (GRM). GRM simulations suggest that as organic rich leachate migrates into the far-field, iron III minerals such as iron hydroxide will dissolve, and reduced iron minerals such as siderite will precipitate due to microbial processes. Batch and column experimental studies have verified this conceptual understanding. Some unexpected processes, such as the presence of nitrate enhancing sulphate reduction, were also observed

Contaminant migration at two low-level radioactive waste sites in arid western United States - A review

Contamination of the unsaturated zone and ground water at the Beatty, Nevada and Richland, Washington low-level radioactive waste sites shows that pathways exist for rapid lateral and vertical migration of contaminants through unconsolidated clastic sediments that comprise the 100 m-thick unsaturated zones of those arid disposal sites. Disposal of liquid wastes at the Beatty site until 1975 may have contributed to rapid migration of contaminants, but negligible amounts of liquid wastes reportedly were disposed at the Richland LLRW site and similar problems of contaminant migration exist. Pathways for vertical migration in the unsaturated zone include fractures and, at Richland, clastic dikes; lateral migration pathways likely are facies-controlled. Disturbance of the disposal sites contributed to increased infiltration of the unlined waste trenches after closure; simulations that used Beatty sample data show dramatic increases in recharge with disturbances necessary to develop the site. Because neither an arid climate nor presence of a thick unsaturated zone offer effective barriers to ground-water contamination, reliance on those factors at proposed sites such as Ward Valley, California and elsewhere is unwarranted.

Low-level radioactive waste site receives go-ahead

Low-level radioactive waste site receives go-ahead

Vegetative cover for low level radioactive waste sites

Low level radioactive waste (LLRW), hazardous, and mixed waste disposal sites normally require some form of plant material to prevent erosion of the soil cover cap. Waste disposal sites are closed and capped in a complex scientific manner to minimize water infiltration and percolation down into the waste material. Turf type grasses are normally used as the principal vegetative cover for most sites. Consequently, the sites require periodic mowing and other expensive annual maintenance practices. The purpose of this 5 year study was to evaluate alternative plant material for use on LLRW sites that can be quickly and easily established and economically maintained, retards water infiltration, provides maximum year-round evapotranspiration, is ecologically acceptable and does not harm the closure cap. The results of the study suggest that two species of bamboo ( Phyllostachys bissetii and Phyllostachys rubromarginata) could be utilized to quickly establish a long lived, low maintenance, final vegetative cover for the waste sites.

Biotic transport of radionuclides from a low-level radioactive waste site.

In the United States, concern for human exposures to radioactivity associated with the disposal of low-level radioactive waste has resulted in a series of regulatory guides, environmental assessments, management practices, and modeling tools. A large number of radionuclide transport processes and mechanisms that may contribute to human exposure have been modeled, using computer programs to make the required calculations. The objective of our work was to evaluate the relevance of potential biological transport processes in the assessment of potential impacts at low-level waste (LLW) disposal sites. As part of this effort, we developed an order-of-magnitude estimate for potential dose to man resulting from biological transport by burrowing animals and by plant translocation at a reference low-level waste site in the arid west. We also made comparative dose-to-man estimates for a more commonly considered human intrusion exposure scenario. Parameter values for defining a reference arid LLW disposal site and biotic transport processes are based on data reported in current literature. Estimates of waste volumes for the western United States are based on information described by the U.S. Nuclear Regulatory Commission in the Draft Environmental Impact Statement in support of 10 CFR Part 61. Our estimates of the dose-to-man resulting from biotic transport are of the same order of magnitude as those resulting from a more commonly evaluated human intrusion scenario. The previously assumed lack of potential importance of biotic transport at LLW sites in earlier assessment studies is not confirmed by our findings. Our results indicate that long-term biological transport processes have the potential to influence LLW site performance, and should be carefully evaluated as part of the impact assessment process.

A Transport Code for Radiocolloid Migration: With an Assessment of an Actual Low-Level Waste Site

AbstractRecently, there is increased concern that radiocolloids may act as a rapid transport mechanism for the release of radionuclides from high-level waste repositories. The role of colloids is, however, controversial because the necessary data and assessment methodology have been limited. To quantitatively assess the role of colloids, the TRACR3D transport code has been enhanced by the addition of the population balance equations. The code was tested against the experimental laboratory column data of Avogadro et al. Next a low-level radioactive waste site was investigated to explore whether colloid migration could account for the unusually rapid transport of plutonium and americium observed. The nature and modeling of radiocolloids are discussed along with site simulation results from the TRACR3D code.