The near field, together with the containment and isolation provided by the geosphere, contributes to the long-term safety provided by a geological disposal facility (GDF) after closure. The different engineered barriers can prevent or limit the release of radionuclides and their migration to the undisturbed host rock or geosphere and are expected to fulfil their post-closure safety functions for many thousands to hundreds of thousands of years. They will continue to contribute to containment after their eventual degradation when there would no longer be confidence that they would continue to fulfil all of their safety functions in their totality. By that time, significant radioactive decay will have occurred, substantially reducing the hazard associated with the wastes. Therefore, demonstration of long-term safety requires an understanding of the evolution of the engineered barriers and the consequences for the generic safety functions that the different barriers provide. This paper provides an overview of the research of the Nuclear Decommissioning Authority Radioactive Waste Management Directorate into the evolution of the near field of a GDF.

A single-crystal X-ray diffraction study of a sample of natural gedrite from North Carolina, USA, with the crystal-chemical formula ANa0.47B(Na0.03Mg0.97Fe0.942+Mn0.02Ca0.04)C(Mg3.52Fe0.282+Al1.15Ti0.054+)T(Si6.31Al1.69)O22W(OH)2, up to a maximum pressure of 7 GPa, revealed the following bulk and axial moduli and their pressure derivatives: K0T = 91.2(6) GPa [K0T' = 6.3(2)]; K0T(a) = 60.5(6) GPa [K0T(a)' = 6.1(2)]; K0T(b) = 122.8(2.6) GPa [K0T(b)' = 5.7(8)]; K0T (c) = 119.7(1.5) GPa [K0T(c)' = 5.1(5)]. Gedrite has a much higher bulk modulus than anthophyllite (66 GPa) and proto-amphibole (64 GPa). All of the three axial moduli of gedrite are higher than those of these two other orthoamphiboles. The greater stiffness of gedrite along [100] is due to its high ANa content, which is almost zero in anthophyllite and proto-amphibole. The much greater stiffness parallel to the (100) plane of gedrite compared with the two other amphiboles is probably due to its high CAl content. A comparison is made with published data available for orthorhombic B(Mg, Mn, Fe) and monoclinic BCa amphiboles to identify correlations between crystal-chemistry and compressibility in amphiboles.

Omsite (IMA 2012-025) is a new mineral from the Correc d'en Llinassos, Oms, Pyrénées-Orientales Department, France. It occurs as bright yellow to amber yellow discoidal tablets, flattened on {001}, which form rosettes typically 50–100 μm in diameter. Omsite generally crystallizes on siderite without associated supergene minerals; it occurs less commonly with glaukosphaerite. Crystals have a vitreous to resinous lustre, and are transparent to translucent. Omsite is not fluorescent in either short-wave or long-wave ultraviolet light. It has an estimated hardness of 3 on the Mohs' scale, is brittle with an irregular fracture, and has one poor cleavage on {001}. The calculated density is 3.378 g cm–3. Crystals are uniaxial (–), with indices of refraction of ω = 1.728(3) and ε = 1.66(1), measured in white light. Pleochroism is ω = orange-yellow, ε = pale orange-yellow; ω > ε. The empirical formula [based on 12 (OH + Cl) p.f.u.] is (Ni1.0992+Cu0.6652+Mg0.107Fe0.0453+)Σ 1.916Fe1.0003+(Sb0.9475+As0.072Na0.029)Σ1.048OH11.967Cl0.033. Omsite crystallizes in space group P, with unit-cell parameters a = 5.3506(8), c = 19.5802(15) Å, V = 485.46(10) Å3 and Z = 2 determined by single crystal X-ray diffraction. The five strongest lines in the X-ray powder diffraction pattern [d in Å, (Irel), (hkl)] are as follows: 4.901, (100), (004); 4.575, (83), (011); 2.3539, (81), (11); 1.8079, (48), (11); 3.781, (34), (103). The crystal structure was solved to R1 = 0.0896 for 356 observed reflections [Fo>4σFo] and 0.1018 for all the 469 unique reflections. Omsite is a layered double hydroxide (LDH) mineral, with a topology consistent with members of the hydrotalcite supergroup and cualstibite group.

The thermal stability of the synthetic iodine analogue of vanadinite, Pb5(VO4)3I, in air has been investigated by in situ high temperature X-ray powder diffraction between 300 and 1070 K. Rietveld refinement of phase fractions shows that breakdown to lead orthovanadate, Pb3(VO4)2, begins at temperatures above 540 K, with complete loss of iodine above 680 K. More than 50 K below the onset of breakdown, the unit-cell parameters of Pb5(VO4)3I show anomalous contraction in the crystallographic x–y plane (reduction of a) which we associate with movement of iodine within the [0001] channels of the structure. The implications of these results for immobilization of 129I in potential apatite-related crystalline radioactive waste forms are discussed.

The heat outputs of higher burn up spent fuels (SF) create problems for disposal in mined repositories, including needs for reduced container loadings and extended pre-disposal cooling. An alternative that is less temperature sensitive is deep borehole disposal (DBD) which offers safety, cost, security and other potential benefits and could be implemented relatively quickly using currently available deep-drilling technology. We have modified our previously proposed version of DBD to be more appropriate for higher burn-up fuels by using smaller (0.36 m diameter) stainless steel containers, a smaller (0.56 m diameter) borehole, and different support matrices. We present the results of new heat-flow modelling for DBD of UO2 and MOX SF with burn ups of 55 and 65 GWd/t showing how temperatures evolve, especially on the outer surface of the containers. Consequences for the performance of the support matrices and the disposal concept are discussed. The thermal modelling indicates DBD is a viable option for higher burn-up SF and could be a practical disposal route for many combinations of fuel types, burn ups, ages and container loadings. Further, the results suggest that DBD of complete fuel assemblies, a desirable option, would be feasible and require much shorter pre-disposal cooling than necessary for disposal in mined repositories.

The new mineral calciolangbeinite, ideally K2Ca2(SO4)3, is the Ca-dominant analogue of langbeinite. It occurs in sublimates at the Yadovitaya fumarole on the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure eruption, Tolbachik volcano, Kamchatka, Russia. The mineral is associated with langbeinite, piypite, hematite, rutile, pseudobrookite, orthoclase, lyonsite, lammerite, cyanochroite and chlorothionite. Calciolangbeinite occurs as tetrahedral to pseudooctahedral crystals, which are bounded by {111} and {11}, and as anhedral grains up to 1 mm in size, aggregated into clusters up to 2 mm across, and forming crusts covering areas of up to 1.5x1.5 cm on the surface of volcanic scoria. Late-stage calciolangbeinite occurs in complex epitaxial intergrowths with langbeinite. Calciolangbeinite is transparent and colourless with white streak and vitreous lustre. Its Mohs' hardness is 3–3½. It is brittle, has a conchoidal fracture and no obvious cleavage. The measured and calculated densities are Dmeas = 2.68(2) and Dcalc = 2.74 g cm–3, respectively. Calciolangbeinite is optically isotropic with n = 1.527(2). The chemical composition of the holotype specimen is Na2O 0.38, K2O 21.85, MgO 6.52, CaO 16.00, MnO 0.27, FeO 0.08, Al2O3 0.09, SO3 55.14, total 100.63 wt.%. The empirical formula, calculated on the basis of twelve oxygen atoms per formula unit, is K2.01(Ca1.24Mg0.70Na0.05Mn0.02Fe0.01Al0.01)S 2.03S3.00O12. Calciolangbeinite is cubic, space group P213, a = 10.1887(4) Å, V = 1057.68(4) Å3 and Z = 4. The strongest reflections in the X-ray powder pattern [listed as (d, Å (I)(hkl)] are 5.84(8)(111); 4.54(9)(120); 4.15(27)(211); 3.218 (100) (310, 130); 2.838 (8) (230, 320), 2.736 (37) (231, 321), 2.006 (11) (431, 341) , 1.658(8)(611,532,352). The crystal structure was refined from single-crystal X-ray diffraction data to R = 0.0447. The structure is based on the langbeinite-type three-dimensional complex framework, which is made up of (Ca,Mg)O6 octahedra (Ca and Mg are disordered) and SO4 tetrahedra. Potassium atoms occupy two sites in voids in the framework; K(1) cations are located in ninefold polyhedra whereas K(2) cations are sited in significantly distorted octahedra. Calciolangbeinite and langbeinite are isostructural and form a solid-solution series.

Diamond and coesite occur in granulites of the Internal Zone of the Rif belt in northwest Africa. Diamond, identified by optical microscopy, electron microprobe analysis, Raman spectroscopy, cathodoluminescence and microstructural electron backscattered diffraction, is present as inclusions up to 20 μm across in garnet, K-feldspar, coesite relics and quartz. Thermobarometric estimates yield P >4.3 GPa and T >1100°C, which corresponds to a depth of formation >150 km. The estimates suggest that the diamond-bearing peridotites and adjacent crustal rocks experienced similar P–T conditions. If this is correct, there is an old (undated) core in the Betic–Rif cordillera and the current models of the tectonic evolution of the area, which are based on 'full Alpine' evolution, must be revised. This discovery provides further valuable information about the complex geotectonic environment of the southeast Spain and north Moroccan collisional orogen.

The Cyprus Natural Analogue Project was carried out due to the requirement to support ongoing laboratory and modelling efforts on the potential reaction of the bentonite buffer with cementitious leachates in the repository engineered barrier system. Although it is known that the higher pH (12.5–13) leachates from ordinary Portland cement will degrade bentonite, it is unclear if this will also be the case for the lower pH (10–11) leachates typical of low alkali cements. Ongoing laboratory and underground rock laboratory programmes, which are currently investigating this, face the obstacle of slow kinetics and the production of short-lived metastable phases, meaning obtaining unambiguous results may take decades. It was therefore decided to implement a focussed natural analogue study on bentonite/low alkali cement leachate reactions to provide indications of the probable long-term reaction products and reaction pathways to provide feedback on the existing short-term investigations noted above and to ascertain if any critical path research and development needs to be instigated now. The results of the analyses presented here, in this short overview of the project, suggest that there has been very limited alkaline groundwater reaction with the bentonite. This is generally supported by both the geomorphological evidence and the natural decay series data which imply groundwater/rock interaction in the last 105 a.

Potassium-rich mafic dykes and lavas from the Highwood Mountains Igneous Province, USA were studied by electron-microprobe and bulk-rock analysis. For the mafic phonolites, compositional trends for olivine and augite phenocrysts and groundmass biotite, alkali feldspar and titanomagnetites are presented and substitution mechanisms discussed. Phenocrysts of biotite and augite in the minettes are also characterized, together with groundmass alkali feldspar and titanomagnetite. The alkali feldspars and biotites are commonly enriched in Ba. Olivine, clinopyroxene and biotite phenocrysts are generally quite magnesium-rich, which is consistent with the primitive natures of the least evolved rocks.

Bulk-rock major-element compositions are combined with modal and microprobe data for the principal phenocrysts to calculate model residual liquid compositions for mafic phonolites, minettes and a syenitic rock. On the basis of phase-equilibria, it is suggested that the main controls of differentiation are polybaric involving crystallization during transport of primary magmas from the mantle for the minettes, and low-pressure differentiation for the mafic phonolites. Whereas magma mixing might have contributed to petrogenesis, many of the disequilibrium features exhibited by clinopyroxene and biotite phenocrysts can also be attributed to pre-existing phenocrysts undergoing decompression melting during magma uprise from its mantle source, followed by rapid crystal growth and episodic volatile loss in sub-volcanic magma chambers.

Some of the illustrative concepts for the disposal of intermediate-level waste in a geological disposal facility in the UK employ a cementitious backfill around the waste packages. The concept for higher strength rocks would use a highly alkaline backfill composed of Portland cement (now known as CEM I), hydrated lime and limestone flour, referred to as Nirex reference vault backfill (NRVB).

This paper reports a study of the extensive leaching of cured NRVB in a range of generic leachant compositions (deionized water, 0.1 M and 1 M NaCl solutions) under flow-through conditions using a flexible wall permeameter. The experiments were designed to run for up to two years and to pass at least 1000 volumes of leachant (defined as the cumulative leachate volume produced/NRVB solid specimen volume) through the NRVB samples. Results for the pH evolution profiles of the leachates and the microstructural analysis of the unleached and leached samples are presented.

New electron-microprobe analyses of mayenite from the Ettringer Bellerberg volcano near Mayen in the Eifel district, Germany have high Cl contents and Raman spectroscopy indicates the presence of OH groups. Neither of these components is included in the generally accepted chemical formula, Ca12Al14O33. A refinement of the crystal structure by single-crystal X-ray methods reveals a previously unrecognized partial substitution. The O2 site which forms one of the apices of an AlO4 tetrahedron (with 3 × O1 sites) is replaced by 3 × O2a sites, which change the coordination of the central Al atom from tetrahedral to octahedral. This substitution is related to partial hydration of Ca12Al14O32Cl2 according to the isomorphic scheme (O2– + Cl–) ↔ 3(OH)–. The revised composition of Eifel mayenite is best described by the formula Ca12Al14O32–xCl2–x(OH)3x (x ∼0.75); the original formula, Ca12Al14O33, is inadequate. The analysed mineral can be considered to consist of endmember Ca12Al14O32Cl2 (62.5 mol.%) and endmember Ca12Al14O30(OH)6 (37.5 mol.%).

A range of potential concepts for the geological disposal of high level wastes and spent fuel are being studied and considered in the UK. These include concepts that use bentonite as a buffer material around the waste containers. The bentonite will be required to fulfil certain safety functions, the most important being (1) to protect the waste containers from detrimental thermal, hydraulic, mechanical and chemical processes; and (2) to retard the release of radionuclides from any waste container that fails. The bentonite should have a low permeability and a high sorption capacity.

These safety functions could be challenged by certain features, events and processes (FEPs) that may occur during the evolution of the disposal system. A consideration of how these FEPs may affect the safety functions can be used to identify and to prioritize the important areas for research on bentonite. We identify these important areas (which include hydration of compacted bentonite, illitization and erosion of bentonite), and describe how they are being investigated in current international research on bentonite.

The Äspö EBS Task Force is a collaborative international project designed to carry out research on bentonite. In 2011, the Nuclear Decommissioning Authority Radioactive Waste Management Directorate joined the EBS Task Force partly to benefit from its collective experience. The work of the EBS Task Force is split into two research subareas: (1) the THM subarea, which includes tasks to understand homogenization of bentonite as it resaturates, to investigate the hydraulic interaction between bentonite and fractured rock, and to model in situ experiments; and (2) the THC subarea, which includes tasks to investigate the issue of understanding transport through bentonite, and to model in situ experiments. In particular, the bentonite rock interaction experiment is a large-scale in situ experiment concerned with understanding groundwater exchange across bentonite rock interfaces, with the objective of establishing better understanding of bentonite wetting. In this paper, we describe our work to model the spatial and temporal resaturation of bentonite buffer in a fractured host rock.

An article by A. C. Kerr and coworkers published in 2010 in Mineralogical Magazine (74, 1027–1036), reviewed an event that was interpreted as the eruption of a basaltic flow on 27th January 2010, at Tor Zawar, Ziarat, Pakistan. The regional and local geology, volcanological aspects, petrography and major-element and trace-element analyses of two samples were presented. On the basis of these data it was proposed that this was a magmatic event and that the lava was derived from the mantle. On the basis of our extensive field work in the this area, and observations at the site of another similar incident that happened almost a year later (in January 2011) ∼300 m north of the first locality, we wish to clarify the geological context and propose an alternative origin.

Our field observations suggest that both events were the result of localized surface melting at the base of metal electricity pylons, and their associated steel cable supports. The metal pylons and cable supports provided a path to earth for lightning discharges into the volcanic conglomerate of the Late Cretaceous Bibai Formation. We propose that this transmitted sufficient energy to melt the outcrop. We disagree with the proposal that the 'lava flows' at Tor Zawar were magmatic events and that the rocks formed are derived from the mantle. Alternatively, we propose that these 'lavas' were produced in a manner similar to fulgurites.

A cementitious backfill has been proposed in many geological disposal concepts for intermediate-level waste and low-level waste in the UK and elsewhere. In this paper, the main features of the chemical evolution of backfill and the associated changes in the near-field pH are illustrated with results from recent work. For example, interaction of the groundwater with calcium silicate hydrate (C-S-H) phases in a backfill is expected to play an important role in the long-term pH-buffering behaviour. Existing experimental data for the dissolution of C-S-H gels are compared with recent experimental results from leach tests on gels of a lower calcium to silicon ratio (C/S) to provide a consistent set of data across the full C/S range. The results confirm that a congruent dissolution point around C/S = 0.8 is approached by leaching from below (i.e. for gels with 0.29 < C/S < 0.8), as well as from above, as reported elsewhere. In addition, a spreadsheet model has been developed to calculate the volume of backfill required at the vault scale to meet specified pH performance criteria. This model includes the major reactions of the backfill with the groundwater, waste encapsulants and waste components. It can also consider the effects of specific waste packages on local pH performance to allow comparison with the vault-scale calculations.