•A discussion of the effects of uranium from seawater on nuclear systems choices.•The requirements necessary to supply the global nuclear energy sector are studied.•Potential flaws have been examined, including legal frameworks within maritime law.•Considerations include feasibility and the environmental implications of deployment.The availability of uranium drives the future of the nuclear energy industry; an upper limit on uranium prices will determine whether it is economically viable to continue utilising the present generation of light water reactors (LWRs). The alternative is a move towards fast reactors, which use less uranium than LWRs, however require substantial investment and development, and might never become economically viable unless uranium prices rise considerably. While terrestrial uranium resources are seen to be limited, there are approximately 4 billion tonnes of uranium in seawater and although uranium only exists at concentrations of around 3.3 ppb, selective extraction has been achieved. Even though several thorough cost estimates of the extraction process have been undertaken, the practicality of the process and the scale on which it would need to be deployed to sustain the nuclear industry is still questionable. This review aims to examine some of the limitations of the current favourite amidoxime braid system, as well as examining possible interactions with existing legal frameworks which have been put in place; in particular those protecting the marine environment. The potential for uranium extraction from seawater is clearly vast, together with the consequences for nuclear technology choices - but the implications of deploying the technology on such a large scale must be considered.Download high-res image (184KB)Download full-size image

Radium-226 is a naturally-occurring radioisotope with potentially significant radiological impact and whose environmental behaviour is of concern. The reactions of tracer (0.1–1 nM) dissolved Ra and its chemical analogue Ba with the surfaces of a range of carbonate minerals have been studied. All of the minerals react with Ra but, whereas calcite, dolomite, strontianite, rhodocrosite, ankerite and witherite all show increased uptake with increasing Ra concentration, suggesting a coprecipitation reaction (hence with phase formation limiting uptake), siderite, magnesite and ankerite show behaviour suggesting simple sorption (with decreasing uptake as Ra concentration increases, or with no dependence on [Ra]). Magnesite, in particular, has a low sorption capacity.Barium has been used at higher (0.1–1 mM) concentrations to enable the use of surface analytical and imaging techniques in addition to bulk uptake measurements. Although the same eight carbonates were studied, measurable uptake occurs only on dolomite, magnesite and siderite. For siderite and magnesite, there is an approximately linear relationship between the increasing solid and solution phase Ba concentrations, suggesting a simple sorption process. Dolomite shows more complex behaviour suggesting simple sorption at the lowest concentrations and phase formation at higher concentrations (>0.4 mmol L−1). The latter observation is consistent with spectroscopic evidence for the formation of witherite. Surface analysis and imaging of the three carbonate substrates that react with Ba show a diversity of behaviour, partly as a result of using natural minerals in these experiments. Witherite is commonly formed as a surface precipitate although the presence of even trace SO42- leads to barite formation. The surface phases display a range of characteristic morphologies, and the surface structure has the effect of templating growth. The presence of even minor amounts of Fe (hydr)oxide phases as alteration products or precipitates on the carbonates is also important, since Ba has a strong affinity for these phases.Highlights► Barium and radium react with carbonate minerals. ► Radium reacts with all the phases studied. ► Barium reacts only with dolomite, magnesite and siderite. ► We study the development of secondary phases formed in these reactions. ► Trace components of the minerals can dictate the outcome of reaction.

•Particulate input is the dominant mechanism for transport of Am, Pu, Cs and 236U.•Seawater circulation and distance control the lag time for radionuclide transport.•Pu and natural uranium do not respond to the redox chemistry in the soil core.•236U showed a potential response to the redox chemistry in the soil core.•236U is a powerful marker for historical and geochemical signals.During the operations at the Sellafield nuclear fuel reprocessing complex, artificial radionuclides are discharged to the Irish Sea under authorisation, where they are dispersed. In this study, the southern distribution and transport of Sellafield derived radionuclides have been investigated. Both natural and artificial radionuclides have been studied in a soil core from the riverbank of the Afon Goch in Anglesey, North Wales. Particulate input is dominant for all artificial radionuclides (including the more soluble 137Cs and 236U) with an estimated lag time of about a decade. The preferential northward seawater movement in the NE Irish Sea limits solution input of 137Cs and 236U to the areas south of Sellafield. The relatively long lag time reflects both the water circulation pattern and distance between the study site in north Wales and the source point in Cumbria. Two redox active zones are observed in the top and the bottom of this core, although there is no evidence for any redistribution of Pu and natural uranium by these redox processes. However, 236U, derived from irradiated uranium, showed variable distribution in the core. This could be a potential response to the geochemical conditions, showing that 236U may be a promising tracer for the environmental processes and a signature of the Sellafield historical discharges of irradiated uranium.

Feldspar minerals are thermodynamically unstable in the near-surface environment and their surfaces are well known to react readily with aqueous solutions, leading to incongruent dissolution at low pH values, but congruent dissolution at neutral and high pH values. Interactions with mineral surfaces are an important control on the environmental transport of trace elements and detrital feldspars are abundant in soils and sediments. However, the interactions of metal ions in solution with the reacting feldspar surface have not been widely explored. The interactions of Pb(II), U(VI) and Np(V) ions with the feldspar surface have therefore been studied. Lead is taken up by the microcline surface at pH 6 and 10, but no uptake could be measured at pH 2. There was measurable uptake of Pb(II) on the plagioclase surface at pH 2, 6 and 10. Uptake always increased with pH. In most conditions, Pb(II) reacts through cation exchange process although, at high pH, a discrete phase, probably hydrocerrusite, is observed by atomic force microscopy (AFM) to precipitate on the plagioclase surface. Supersaturation with hydrocerrusite in these conditions is expected from thermodynamic calculations. Uptake of uranyl ion (UO22+), generally through surface complex formation, could only be measured at pH 6 and 10. At pH 6 and an initial U(VI) concentration above 21.0 μM, precipitation of becquerelite (Ca[(UO2)3O2(OH)3]2·8H2O), identified by AFM and characterised by grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy, is observed on plagioclase. The U(VI) concentration range in which becquerelite precipitation begins (dissolved U(VI) 1–5 μM) is consistent with that predicted from thermodynamic modelling. On plagioclase feldspar, secondary ion mass spectrometry showed diffusion of uranium into the altered surface layer. Uptake of the neptunyl ion (Np(V)) was found at pH 6 and 10 for microcline and at pH 2, 6 and 10 for plagioclase, and was generally lower than uptake of U(VI). By combining batch sorption experiments with imaging and surface analysis, and thermodynamic modelling, it has been possible to gain a mechanistic insight into the reactions of the feldspar surface with metal ions in solution.