In recent years there has been an increasing awareness of the radiological impact of non-nuclear industries that extract and/or process ores and minerals containing naturally occurring radioactive material (NORM). These industrial activities may result in significant radioactive contamination of (by-) products, wastes and plant installations. In this study, scale samples were collected from a decommissioned phosphoric acid processing plant. To determine the nature and concentration of NORM retained in pipe-work and associated process plant, four main areas of the site were investigated: (1) the 'Green Acid Plant', where crude acid was concentrated; (2) the green acid storage tanks; (3) the Purified White Acid (PWA) plant, where inorganic impurities were removed; and (4) the solid waste, disposed of on-site as landfill. The scale samples predominantly comprise the following: fluorides (e.g. ralstonite); calcium sulphate (e.g. gypsum); and an assemblage of mixed fluorides and phosphates (e.g. iron fluoride hydrate, calcium phosphate), respectively. The radioactive inventory is dominated by 238U and its decay chain products, and significant fractionation along the series occurs. Compared to the feedstock ore, elevated concentrations (< or =8.8 Bq/g) of 238U were found to be retained in installations where the process stream was rich in fluorides and phosphates. In addition, enriched levels (< or =11 Bq/g) of 226Ra were found in association with precipitates of calcium sulphate. Water extraction tests indicate that many of the scales and waste contain significantly soluble materials and readily release radioactivity into solution.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to study the surface of a depleted uranium (DU) disc immersed in a Ca-phosphate solution for 182 days. The weathering solution contained 2.49·10−3 M calcium and 1.05·10−3 M phosphate, representing enhanced pore water concentrations of agricultural soils. The TRLFS results clearly show that meta-autunite, a U(VI) phosphate, has formed during low temperature alteration of the DU disc. This secondary U(VI) mineral phase was identified using a fingerprinting procedure by comparing it with TRLFS-spectra from an in-house U(VI) TRLFS database, including U(VI) oxides, U(VI) hydroxides, U(VI) sulphates and U(VI) phosphates. Its TRLFS spectrum is characterized by six fluorescence emission bands at 486, 501, 522, 546, 573, and 601 nm, and two fluorescence life times of 50±5 ns and 700±25 ns.

This paper describes the only documented occurrence of radioactive scale in China Clay refining and the advances that have been made in dealing with the problem since it was first discovered in the late 1990s. Extensive characterisation studies have established the mineralogy, crystallography, chemical composition and radionuclide inventory of scale formed at each stage of the refining process. The dominant isotopes present are 226/228Ra, incorporated by co-precipitation in barium sulphate, and members of their decay chains, notably 210Pb and 210Po. Following decontamination trials, a decision was made to adopt ultra high pressure water jetting as the preferred removal method. A state of the art facility has been constructed in Cornwall and has recently entered service. Decontamination gives rise to a slurry comprising scale, associated minerals, corroded metal and large quantities of water. Research to define a suitable immobilisation matrix identified a highly durable cemented product with excellent leach resistance. Full-scale specimens have now been prepared, completing the plant refurbishment cycle. Many of the techniques described in this paper are applicable to other mineral wastes and radioactive contamination problems in complex industrial plant.

Incorporation of radioactive isotopes during the formation of barite mineral scale is a widespread phenomenon occurring within the oil, mining and process industries. In a series of experiments radioactive barite/celestite solid solutions (SSBarite–Celestite) have been synthesized under controlled conditions by the counter diffusion of 226Ra, Ba2+, Sr2+ and SO42− ions through a porous medium (silica gel), to investigate inhibiting effects in Ra uptake associated with the introduction of a competing ion (Sr2+). From characterization studies, the particle size and the morphology of the crystals appear to be related to the initial [Sr]/[Ba] molar ratio of the starting solution. Typically, systems richer in Sr produce smaller sized crystals and clusters characterized by a lower degree of order. The activity introduced to the system is mainly incorporated in the crystals generated from the barite/celestite solid solution as suggested by the activity profiles of the hydrogel columns analysed by γ-spectrometry. There is a relationship between the initial [Sr]/[Ba] molar ratio of the starting solution and the activity exhibited by the synthesized crystals. An effective inhibition of the 226Ra uptake during formation of the crystals (SSBarite–Celestite) was obtained through the introduction of a competing ion (Sr2+): the higher the initial [Sr]/[Ba] molar ratio of the starting solution, the lower the intensity of the activity peak in the crystals.

Depleted Uranium (DU) contamination now exists in diverse environments, for example, agricultural land in Kosovo, and desert in Kuwait due to its use in munitions, and also in the sea following weapons testing. However, the environmental fate of DU following corrosion and oxidation of fragments is not well known. Consequently, a need has arisen for studies on the corrosion of DU under different geochemical conditions. To date, the only documented secondary mineral formed as a result of the alteration of DU metal is schoepite ((UO2)8O2(OH)12(H 2O) 12), which is a relatively unstable phase [1,2]. Other solid phases are likely to be formed in situations such as those listed above. Discs of DU metal from unfired penetrators have been artificially weathered over six months, in order to quantify corrosion rates and to investigate the development of secondary alteration products on the corroding surface. The solutions employed were Ultra High Quality (UHQ) water, as a control, a calcium phosphate-rich solution representing agricultural soils and a silica-rich solution representing desert conditions. XRD results show that the first phase formed in UHQ water is UO2 followed after one week by schoepite and, after four months, studtite (UO4·4H2O). Surface analysis of the DU in the calcium phosphate solution detected uranyl phosphate hydrate ((UO2)3PO4·4H2O) after one week with schoepite after eleven weeks. The discs in this solution showed little visible sign of corrosion and the mass did not change significantly during the experiment, suggesting passivation of the surface. XRD analysis of DU in the silica-rich solution detected a range of uranyl oxides from UO2 to UO3, but to date no other minerals have been observed. Corrosion of DU in the silica solution was more rapid and after six months 20% of the original mass had been lost.

This paper provides a brief perspective on synthetic, phosphate-based waste forms for high level radioactive waste (HLW). Evidence in support of their long-term stability is then discussed by reference to the degradation of natural monazites with emphasis on the fate of released uranium, thorium and the rare earths (REE). It is apparent that the REE can be mobilized and fractionated at temperatures anticipated in a HLW repository (similar to 200 degreesC). This provides an indication of the likely fate of the trivalent actinides (Am(III), Cm(III)) if incorporated in similar matrices. Thorium., though released on alteration of monazite, tends to re-concentrate locally in secondary, microcrystalline phases. In relative terms, U is readily removed from monazites. Although it can be re-concentrated in alteration products, the potential exists for substantial loss of U to groundwater. The findings of this research have important implications for the performance of radioactive waste disposal systems where there is a clear need for improved chemical data to describe the precipitation-dis solution of phosphate phases. It is concluded that monazite-like ceramics designed for the containment of HLW will retain tetravalent actinides but may release uranium in response to natural degradative processes.

Demonstrating confidence in the long-term performance of a spent fuel disposal site is largely dependent on developing an adequate understanding of the geological barrier system and its evolution. However, performance assessment modelling is usually based solely on estimates of present-day groundwater fluxes that cannot be assumed to be representative of time scales on the order of tens to hundreds of thousands of years. The uncertainties associated with changing boundary conditions are particularly important at high latitudes and in coastal regions owing to the effects of climate change. Palaeohydrogeology, using mineralogical, isotopic and hydrochemical evidence of past events provides a firmer scientific basis for predicting future trends. In this respect, the Palmottu study is unique among natural analogue investigations in that it seeks to establish the effects of glaciation on an ancient uraninite deposit hosted in crystalline, igneous rock. Owing to its geological and geographical setting, the results are of direct relevance to repository projects in Finland, Sweden and Canada.

The results of in situ tests conducted at the HADES underground laboratory, Mol, Belgium, indicate significant reaction between Boom Clay and ordinary Portland cement over a period of 18 months. Mass transfer of calcium, magnesium, aluminium, iron, silicon and sulphur leads to the development of a distinct zonal structure extending 100–250 μm into both the cement and the clay. The associated mineralogical changes have modified the microstructure of the altered region and there is clear evidence of increased porosity in the zone of portlandite dissolution. Additionally, experiments conducted at 85°C show the presence of a narrow Mg-Al-Si rich band in the clay close to the contact. Analyses indicate the formation of a di-phasic (Mg-aluminate hydroxide and Mgsilicate hydroxide) gel with low crystallinity and compositions close to hydrotalcite and sepiolite, respectively. Reactive transport modelling has been used to simulate phase transformations within the active region and relate these to porosity changes based on simple molar volume considerations. Given the close coupling of mineral chemistry and microstructure in cement±clay systems, such an approach is regarded as essential if reliable estimates are to be made of long-term reactivity.

The paucity of data for safety critical species is commonly cited as the reason why relatively few thermodynamic parameters are employed directly in conventional safety calculations. This paper provides an overview of the information required and describes a number of data estimation methods that have been employed with considerable success in the geological sciences. Each is based upon a thermodynamic representation of the processes known to take place during rock-water interaction. It is hoped that in the future such techniques will allow a shift of emphasis from the collection of empirical "sorption constants" to a more fundamental appraisal of trace element immobilisation in waste disposal systems.

The migration of uranium through siliceous porous media has been investigated by conducting a series of core flood experiments in conjunction with the development of predictive coupled chemical transport models. Initial investigations made during the programme have demonstrated that under oxidising conditions, at pH≈5–6 with NaCl concentrations ≈0.3 mol dm−3, uranium is strongly retarded by adsorption to a Clashach Sandstone matrix. Sorption has been shown to be largely reversible, dependent on the absolute concentrations involved and on the finite sorptive capacity of the rock. Comparative experimental and modelling studies have also demonstrated the sorptive behaviour of the Clashach Sandstone to be close to that of amorphous silica. Recent work has focused on assessing the role of EDTA and cellulose degradation products in enhancing uranium mobility by complexation/chelation. Laboratory scale migration experiments involving radio-labelled EDTA and saccharic acid have been supported by batch sorption studies to investigate the behaviour of the U–EDTA-silica and U–saccharic acid-silica systems. In order to obtain unequivocal comparisons of the rates of uranium migration in the presence and absence of the organic complexant, parallel column floods have been carried out such that intact cores of Clashach Sandstone have been flooded with waters from the same reservoirs at carefully controlled flow rates. Geochemical modelling techniques have been used to assess the chemical speciation of the waters, to describe the sorption behaviour observed in the batch sorption studies and, where appropriate, derive model specific data to allow predictive coupled chemical transport modelling of the migration experiments. It is shown that, for a pre-equilibrated uranium-organic system, the use of conventional techniques encompassing complexation in the aqueous phase and reversible adsorption of organically-bound species would give a reasonable approximation of the system. Conversely, where uranium is introduced ahead of the organic plume, re-mobilisation is severely constrained by slow desorption kinetics. The results point to the need to consider the sequence of radionuclide interactions with organic waste components in formulating models used in performance assessment.