This paper provides a summary of the research programme undertaken in support of the Low Level Waste Repository's 2011 environmental safety case (ESC). The programme has been developed, based on an understanding of safety issues and the requirements of the ESC. The research requirements to underpin the safety case have been identified by means of an auditable process, and subjected to scrutiny by both the regulators and a peer review group. Key research priorities for the future are identified.

A phosphate-rich carbonate nodule from carboniferous mudstones has been studied by wet chemistry, X-ray diffraction, and electron microprobe. Partial heavy-liquid separation has enabled characterization of the phosphate phase as francolite (carbonate fluorapatite) with a composition Ca10(PO4)5·59(CO3)1·00((OH)1·49F2·10). Diffractometer data for this mineral is presented and cell dimensions are calculated as a = 9·349 Å, c = 6·887 Å. with c/a = 0·737. The problem of the structural positioning of carbon in francolite is discussed.

The francolite is seen in thin section as a structureless groundmass enclosing siderite spheru-lites. Electron microprobe X-ray distribution photographs for P, Al, Si, Mg, and Fe show the relationship of these two phases to quartz, pyrite, and at least two clay minerals. One of the latter is intimately mixed with francolite.

Possible origins of phosphatic nodules are discussed. Textural evidence in the present case strongly suggests that the francolite is concretionary and formed during early diagenesis possibly by replacement of earlier calcite. Phosphate was probably derived from protein degradation, which also maintained the alkaline pH necessary for francolite formation.

A single crystal of natrojarosite, NaFe3(SO4)2(OH)6, was investigated by single-crystal X-ray diffraction at high-pressure conditions (up to 8.8 GPa) using a diamond-anvil cell. The unit-cell parameters were determined at 11 different pressures and no indications of a phase transition were found up to the maximum pressure reached. The volume and axial moduli were fitted to a third-order Birch–Murnaghan equation-of-state which gave the following values: V0 = 769.6(2) Å3, KT0 = 50.6(9) GPa, K' = 9.9(4); a = 7.3172(6) Å, KT0 = 104(2), K' = 7.6(9); c = 16.5965(20) Å, KT0 = 24.6(4) and K' = 7.1(2). The crystal structure of natrojarosite was refined at seven different pressures up to 8.779(11) GPa [a = 7.3170(4), c = 16.5955(5) Å and V = 769.46(9) Å3 in Rm at 0.00010(1) GPa and a = 7.1594(8), c = 15.6003(17) Å and V = 692.49(8) Å3 at 8.779(11) GPa]. The structural analysis shows that the 12-fold Na polyhedron accommodates most of the deformation by a large volume decrease (14%) and strong polyhedral distortion (63%). Our results indicate that natrojarosite has the most compressible structure of the supergroup studied so far, and has a very strong axial anisotropy.

Tantal-aeschynite occurs as idiomorphic metamict crystals in the Raposa pegmatite at São José do Sabugí, Paraíba State, NE. Brazil. Morphological data, microscopic properties, and differential thermal analysis results are given. Electron-microprobe analyses yielded a formula: {Ca0·28(Yt,Ln)0·425(Th,U)0·11}(Ta0·75Ti0·62Nb0·595Fe0·05)O6. Yttrium is the predominant rare-earth element, with cerium and neodymium as most abundant lanthanides. The tantal-aeschynite unit cell has (after heating) a 5·34, b 10·97, c 7·38 Å. An indexed X-ray powder pattern (similar to that of aeschynite) is presented.

Stable perovskite and metastable post-perovskite NaCoF3 were deformed in pure-shear geometry in a deformation-DIA press with radiographic monitoring of the sample strain. In isothermal experiments where there was no transformation, post-perovskite was found to be 5 times weaker than perovskite. In temperature-ramping experiments where post-perovskite transformed to perovskite during the deformation experiment the initial post-perovskite sample was 5–10 times weaker than perovskite under comparable conditions and their strengths converged during the transformation, being equal on completion of the transformation. These results confirm recent findings which show that postperovskite is weaker than perovskite, regardless of the prior history of the sample.

Aguilarite, Ag4SeS, occurs in a hydrothermal vein deposit associated with sphalerite, chalcopyrite, galena, and native silver. Physical and chemical data agree with descriptions from Guanajuato (type locality). Differential thermal analysis of synthetic material indicates an inversion temperature of 122±1 °C. The mineral crystallized late in the paragenetic sequence, probably slightly above 200 °C.

Mössbauer spectroscopy has been used to identify the iron-containing products that are formed during the thermal decomposition of ankerite in a CO2 atmosphere. The decomposition takes place in three stages and evidence is produced to show that the first stage involves decomposition of ankerite to yield a periclase-wustite solid solution, (Mg,Fe)O, along with calcite and CO2, the periclase-wustite then reacting with CO2 to produce magnesioferrite (MgFe2O4) and CO. In the second stage the magnesioferrite and calcite react to produce periclase and dicalcium ferrite. The third stage does not involve reaction of Fe-containing phases and corresponds to the decomposition of calcite to CaO.

Degradation of contaminant hydrocarbons in groundwater by microbially mediated oxidation, linked to the reduction of electron acceptors, is fundamental to the strategy of ‘monitored natural attenuation’ (MNA) for oxidizable hydrocarbons, which is increasingly being adopted at polluted aquifer sites throughout Europe and North America. Commonly, oxygen is depleted and following the reduction of nitrate, solid-phase Fe oxides become the dominant electron acceptors. Arsenic, associated with Fe and Mn oxides in soils and sediments, may therefore be mobilized to groundwater and pose an additional threat to environmental receptors. In a pilot study of three aquifers in England, we have examined the extent to which arsenic is released to groundwater under Fe(III)-reducing conditions imposed by contaminant hydrocarbons. Results show that arsenic is locally mobilized in the Chalk to <10 μg/1, in Quaternary gravels to 70 μg/1 and in the Triassic sandstones to 160 μg/1. At the Chalk and Quaternary gravels sites arsenic mobilization is demonstrably linked to reduction of Fe- and Mn-oxides. This is not so at the Triassic sandstone site, where release of arsenic is related to elevated bicarbonate alkalinity. Redox-driven arsenic mobilization at other Triassic sandstone locations is possible. Further work is required on the solid-phase sources of arsenic in the aquifers, and to relate the hydrochemical observations to groundwater hydraulic conditions.

A range of authigenic sedimentary chlorites from sandstones has been studied by analytical transmission electron microscopy. Selected area (single crystal) electron diffraction patterns are of the Ib (β = 90°) polytype confirming the earlier observations of Hayes (1970).

TEM analyses show all samples to be relatively rich in both Al and Fe. In the general formula (Mg,Fe,Al)n [Si8−xAlxO20](OH)16, x varies between 1.5 and 2.6; Fe/(Fe + Mg) between 0.47 and 0.83 and n between 10.80 and 11.54. Octahedral Al is close to 3 in this formulation and Fe2+ predominates over Fe3+. Swelling chlorites have significantly different compositions which are consistent with smectite/chlorite interstratifications.

The Ib (β = 90°) polytype appears to be stable under conditions of moderate to deep burial. It replaces berthierine and swelling chlorites formed at lower temperatures. As commonly seen in grain coatings, however, it precipitates from porewater; solutes probably being contributed from several mineral decomposition reactions.

In order to be able to use the nature and scale of the exsolution microstructures developed in titanomagnetites as quantitative indicators of thermal history, it is necessary to have available accurate diffusion data for the system. Diffusion data for pure magnetite and Ti-poor titanomagnetites are available, but no data for diffusion in the centre of the solid-solution series exist. In order to obtain values for the activation energy (ΔE) and the pre-exponential factor (D0) for the interdiffusion of Fe and Ti in ulvöspinel-rich titanomagnetites, the natural microstructures developed in titanomagnetites from the Taberg intrusion, Sweden, were homogenized over a range of temperatures from 490 to 730 °C. From the model describing homogenization, values of 49.8 kcal mole−1 and 2.38 × 10−3 cm2 s−1 were calculated for ΔE and D0 respectively. Although the results obtained from these homogenization experiments are slightly less accurate than those which could be obtained by more conventional methods, the homogenization technique has several advantages which outweigh this drawback, namely the ease with which the experiment can be performed and the fact that the diffusion data can be obtained at significantly lower temperatures than is usually possible with more conventional methods.

The densification of pure magnesia was examined along with mixtures containing 0·5 and 1·0 mol % of calcium oxide and forsterite. The sintering behaviour at temperatures between 1400 and 1800 °C was studied and measurements made of changes in shrinkage, porosity, bulk density, and grain size for sintering times of up to 8 h at sintering temperature. It was found that both the 0·5 and 1·0 mol % additions enhanced the sintering of pure magnesia in the temperature range 1500–1700 °C Increased grain growth was found for mixtures containing forsterite but little change occurred for mixtures containing lime. Examination of the grain growth data showed that the mixtures obeyed a relationship: Time at temperature × Constant = (grain size)n, where n = 2 for the grain growth of pure magnesia and mixtures containing lime, but n = 3 for mixtures of magnesia with additions of a silicate such as forsterite. A value of 78 kcal/mole was obtained for the grain growth of pure magnesia, which agrees with other researches.

The extent of the solubility of lime in periclase for each lime-magnesia mixture at each temperature was also examined using electron probe analysis and related to the sintering behaviour observed for these mixtures.