No description available.

No description available.

No description available.

A global legacy of radioactively contaminated land exists as a result of nuclear fuel cycle operations. Demonstration of the safe management of the UK nuclear legacy, including contaminated land, is important whilst the long term fate of legacy waste remains uncertain and the UK is moves towards new nuclear power. One aspect of nuclear contaminated land research focuses on the immobilisation of intermediate and long lived radionuclides that are mobile in groundwater and are migrating in the environment. At Sellafield nuclear facility, UK, strontium-90 and technetium-99 are found as co-contaminants in groundwater alongside the most abundant non radioactive contaminant, nitrate. Their differing radiochemical behaviour and the presence of nitrate presents a challenge for remediation strategies. Bioremediation has the potential for in-situ immobilization of 99Tc via reduction from mobile Tc(VII) to less mobile Tc(IV) concurrent with Fe(III) reduction. In this project bioreduction processes were investigated in sediment microcosms and model systems under variable pH and nitrate conditions and using microorganisms representative of the Sellafield site. Sediment bioreduction occurred via stimulation of the natural microbial community. Denitrification resulted a delay in the onset of metal reduction followed by a raised pH. At the mildly acidic pH of the natural sediments, a nitrate concentration of 100 mM caused bioreduction to stall. However, at pH 7, reduction of 100 mM nitrate resulted in a final pH > 9 and alkaline Fe(III) reduction. In bioreduced sediments, the microbial ecology was dominated by nitrate reducing microorganisms and Fe(III) reducing enrichment cultures were necessary to identify relevant alkaline Fe(III) reducing bacteria. Enrichment cultures isolated a novel alkali tolerant Fe(III) reducing Serratia sp. with a growth range of pH 4 to 9. Increased pH resulting from denitrification decreased the mobility of Sr2+ via increased sorption to mineral surfaces. X-ray absorption spectroscopy confirmed Sr2+ incorporation into carbonate mineral phases above pH 8.5. Model systems showed reductive removal of 99Tc from solution by an Fe(II) bearing mineral assemblage at both pH 7 and 9. In contrast Sr2+ remained in solution at pH 7 and precipitated as SrCO3 at pH > 8.5. This study for the first time demonstrates the effects of high nitrate on pH in Sellafield type sediments, alkaline Fe(III) reduction by a Serratia sp, the incorporation behaviour of Sr2+ during sediment bioreduction and the behaviour of Sr2+ and 99Tc in novel Fe(II) mineral bearing model systems. These findings improve the understanding of radionuclide migration at contaminated sites and inform possible engineered bioremediation scenarios.

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The Enhanced Actinide Removal Plant (EARP) located at Sellafield, is a key facility for processing nuclear effluents in the UK. The EARP process decontaminates radioactive waste effluent by inducing the coprecipitation of Fe(III) along with any radionuclides in solution. The resulting radioactive solid phase is then separated from the decontaminated aqueous phase by ultrafiltration processes over several weeks. In the future the EARP facility's role will be expanded to treat effluents produced from nuclear decommissioning activities. However there remains a limited understanding around the mechanisms of radionuclide removal from solution and subsequent sequestration within the solid phase under conditions relevant to such industrial effluent treatment facilities. In this work, the fate of U(VI) and Th(IV) were investigated during the EARP process. XRD and TEM analyses revealed that the solid product from the EARP coprecipitation process was 2-line ferrihydrite which transformed over time to form hematite, with some goethite formation observed in the Th containing system. During this coprecipitation process U was initially removed from solution by adsorption to ferrihydrite as a bidentate, edge-sharing surface complex associated with ternary carbonate complexes. As the U containing system was aged, a maximum range of 61 - 75% U became consistently incorporated within the newly formed hematite phase for a wide range of systems containing 6 orders of magnitude total U:Fe molar ratio. Such a constant proportion of incorporated U suggests that this incorporation occurs during a particle mediated mechanism of hematite growth, such as oriented attachment. Interestingly, Th was removed from solution during the EARP coprecipitation process by a combination of both adsorption and occlusion mechanisms. EXAFS analyses revealed that the local coordination environment of Th associated with the solid phase altered considerably with increased aging time, and correspondingly Th became increasingly recalcitrant to remobilisation over time suggesting the formation of further occluded or even incorporated Th species within the transforming iron (oxyhydr)oxide phases. This thesis progresses the fundamental understanding of radionuclide interactions with iron (oxyhydr)oxide phases during coprecipitation and aging processes under conditions relevant to industrial waste treatment processes such as EARP.

The Enhanced Actinide Removal Plant (EARP), located on the Sellafield site, is one of the UK's most crucial radioactive effluent treatment plants. EARP removes actinides and select fission products from routine reprocessing effluents by association with a ferric iron oxyhydroxide floc, which is precipitated from acidic effluent streams by the addition of NaOH. The effluent compositions that EARP receives will change in character as the Sellafield site transitions from its current routine reprocessing operations to post-operational clean-out and accelerated decommissioning activities over the next few years. An enhanced understanding of the iron oxyhydroxide formation processes occurring in EARP would help underpin optimisation of current plant efficiency and allow better prediction of changes in efficiency as effluent composition varies. In this study, iron oxyhydroxide formation, properties and evolution with time under EARP-relevant conditions were characterized. These processes were investigated in a pure ferric nitrate system and systems with added sulfate, phosphate and boric acid using a range of techniques including SAXS, TEM and FTIR. In all the experimental systems the iron oxyhydroxide floc was composed of nanoparticulate ferrihydrite aggregated into extensive mass fractal structures. In situ SAXS experiments showed that formation proceeded via a precursor cluster pathway whereby Fe(III) clusters ~ 0.45 nm in radius form rapidly at pH 0.12 - pH 1.5 upon dropwise addition of strong NaOH to the acidic effluent simulants. Further analysis indicates these clusters are Fe13 Keggin clusters, which have previously been shown to be an important structural motif in the ferrihydrite structure. With further pH increase, cluster aggregation occurs along with precipitation of low molecular weight Fe(III) species (mostly monomers), leading to formation of ferrihydrite nanoparticles which preserve the Keggin cluster in the core. Phosphate, sulfate and boric acid exhibit varying interactions with the solid phase throughout the formation process, with both inner and outer sphere adsorption observed for different species. Ageing experiments show that the ferrihydrite floc readily undergoes transformation leading to predominantly hematite formation, except in the presence of phosphate (concentrations > 10 ppm) where transformation is entirely inhibited due to phosphate adsorption to the floc. These results progress the fundamental understanding of the iron oxyhydroxide formation and ageing processes occurring in EARP.

A number of leaks of radioactive liquors to ground are known to have occurred from several plant buildings, vaults and disposal trenches within and around the Separation area at the Sellafield nuclear site over the past 50 years1. The most significant of these leaks have occurred from the Magnox Silo, the Caesium Extraction Plant, the Magnox Reprocessing Pump House, the Sludge Storage Tanks, the Burial Pits and the Medium Active Evaporation and Thermal Denitration Plant. The radioactive contamination will be accompanied by other components of spent fuel reprocessing, including inorganic salts from neutralised acids, solvents and other organic compounds along with the typical contaminants commonly associated with large industrial activity such as heavy metals, fuel, oils, degreasing agents etc. The research in this thesis describes the effects of common industrial contaminants on the behaviour of Cs and Sr sorption to bentonite and montmorillonite clay minerals. Batch sorption experiments of Cs and Sr uptake onto bentonite and montmorillonite in a number of complex systems were investigated as follows: 1. Initial batch sorption experiments investigating the normal behaviour of the clay minerals. 2. Introduction of anthropogenic organic ligands EDTA, NTA and picolinic acid into the system and their influence on Sr and Cs uptake. 3. Time dependent studies investigating the effect that residence time of the anthropogenic organic ligands has on the sorption properties of montmorillonite and bentonite. 4. Quaternary systems where simulant Magnox sludge equilibrated water, at a number of concentrations, was introduced to ternary systems containing anthropogenic organic ligands. 5. Time dependent studies investigating the effect of hydrocarbons TCE, toluene and naphthalene on the uptake of Cs and Sr to bentonite and montmorillonite. The batch sorption experiments show that the presence of anthropogenic organic ligands reduces the uptake of Cs and Sr by both montmorillonite and bentonite. It is also shown that the presence of simulant Magnox sludge in quaternary systems can also reduce the uptake of Cs and Sr, with significant reductions in sorption observed for Sr sorption in EDTA quaternary systems. Further, the uptake of Cs and Sr to bentonite and montmorillonite appears to decrease with increasing anthropogenic organic ligand residence time. This suggests that the ligands are altering the surface of the clay minerals reducing the number of available binding sites. The influence of hydrocarbons shows a significant decrease in sorption after 3 months for Cs and Sr sorption to montmorillonite. There were no further significant changes for all other hydrocarbon systems investigated.

The first comprehensive analysis of surface waters in the Labrador Sea for 236U was completed via Accelerator Mass Spectrometry. Through the analysis of 236U the method for AMS measurement was fine-tuned to allow for more precise results. Surface samples for the anthropogenic isotopes 137Cs and 129I were also collected along with two depth profiles of 129I. Samples were also collected in the Beaufort Sea and analyzed for the aforementioned isotopes. It was found that anthropogenic 129I from reprocessing plants is easily discernible at different concentrations among water bodies in both the Labrador and Beaufort Sea. 137Cs in surface waters is close to global fallout levels with no discernable influence from reprocessing plant inputs, but follows a similar trend to that of 129I with depth in the Beaufort Sea. 236U among surface waters in the Labrador Sea did not follow the same trends as 129I but had concentrations indicative of a mix of global fallout as well as reprocessing plant influenced waters. 236U samples from the Beaufort Sea were contaminated by an unknown source of 236U and were inconclusive but were reproducible and allowed for continued development of the AMS analysis methodology.

The Environment Agency are responsible for the regulation of radioactive substances in England, which is a highly controversial area to regulate due to the public perception regarding the associated environmental and health impacts. This is further complicated by the Environment Agency’s primary aim of contributing towards sustainable development, which is another controversial and contested concept. The principles of good regulation require a proportionate approach, which can be considered a key component of sustainable development also. However, published literature asserts that the regulation of radioactive discharges is disproportionate, which lacks verifiable data on the regulatory compliance costs and impacts imposed. This also implies that the regulation may not contribute towards sustainable development, which is compounded by the ambiguity of this requirement in the regulatory framework. This thesis therefore seeks to evaluate whether the Environment Agency is achieving its primary aim of contributing towards sustainable development in its regulation of radioactive discharges. To this end, this study sought to identify the interpretation of sustainable development that the law, policy and guidance for the regulation of radioactive discharges requires the Environment Agency to adhere to, and then collect data to assess whether this is being implemented. To achieve this, the law, policy and guidance for the regulation of radioactive discharges has been mapped on to an enhanced sliding-scale of sustainable development interpretations. This has revealed that the regulatory framework drives the Environment Agency to adhere to the newly developed interpretation of stronger sustainability, which requires a proportionate approach to be applied within the limitations of the environment. The regulation applied to Sellafield’s radioactive discharges has then been assessed against this stronger sustainability paradigm. The data collected confirms discharges are within environmental limits and that the regulation has resulted in direct compliance costs of £120 million between 2002 and 2009 without yielding any benefit to the environment in terms of a reduction in collective dose. The measured costs and benefits have been supplemented by a qualitative analysis of impacts that cannot be quantified, and these reinforce the contention that the regulatory approach at Sellafield is disproportionate and therefore inconsistent with stronger sustainability. A likely cause of the disproportionate regulatory approach is attributed to stakeholder and political pressures. Improvements have been proposed to address the disproportionate approach, which have already influenced the removal of some discharge limitations.