The disposal of radioactive wastes underground

Nuclear power is strategically and quantitatively an important contributor to global electricity generation capacity and produces a small amount of potentially highly hazardous wastes that require careful management. The accepted solution for disposing of higher activity and longer-lived radioactive wastes from the nuclear power industry and other sources is engineered emplacement in deep geological disposal facilities (GDFs), situated many hundreds of metres underground. The first purpose-built GDFs for the most active of these wastes (used nuclear fuel and high-level wastes) will be operational in about ten years time in a few countries, with most other countries (including the UK) developing such facilities during coming decades. This article reviews the conceptual basis for geological disposal, examines how long-term safety is provided, considers the geological challenges to developing GDFs and the uncertainties that have to be managed, and looks in more detail at some of the most advanced design concepts. Because the issue of forecasting GDF evolution and behaviour over very long time periods lies at the core of geological disposal, particular emphasis is placed on matching containment requirements with diminishing hazard potential over many thousands of years. The article concludes with a commentary on current developments in the UK geological disposal programme.     

El Niño-Southern Oscillation impacts on winter winds over Southern California

Changes in wintertime 10 m winds due to the El Niño-Southern Oscillation are examined using a 6 km resolution climate simulation of Southern California covering the period from 1959 through 2001. Wind speed statistics based on regional averages reveal a general signal of increased mean wind speeds and wind speed variability during El Niño across the region. An opposite and nearly as strong signal of decreased wind speed variability during La Niña is also found. These signals are generally more significant than the better-known signals in precipitation. In spite of these regional-scale generalizations, there are significant sub-regional mesoscale structures in the wind speed impacts. In some cases, impacts on mean winds and wind variability at the sub-regional scale are opposite to those of the region as a whole. All of these signals can be interpreted in terms of shifts in occurrences of the region’s main wind regimes due to the El Niño phenomenon. The results of this study can be used to understand how interannual wind speed variations in regions of Southern California are influenced by the El Niño phenomenon.     

Alteration of platinum-group minerals and dispersion of platinum-group elements during progressive weathering of the Aguablanca Ni–Cu deposit, SW Spain

The distribution, mineralogy and mobility of the platinum-group elements (PGE) in the surface environment are poorly understood. This study of the lower, less altered and upper, more altered gossan, overlying the Aguablanca Ni–Cu-(PGE) magmatic deposit (Spain), has shown that the platinum-group minerals (PGM) are progressively oxidised and dispersed into iron oxides that form the gossan. A combination of the characterization of PGE in host PGM, using a scanning electron microscope, and measurement of PGE at lower concentrations in host iron oxides, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), has for the first time allowed the total distribution of the PGE within a gossan to be documented. This study has revealed a complete in situ alteration and dispersion sequence of the PGM including (1) breakdown of both the more stable Pt-arsenides, Pt/Pd-tellurides and the less stable bismuthotellurides, (2) formation of partially oxidised PGM, (3) development of a wide range of oxidised Pt- and Pd-bearing phases, (4) subsequent formation of Fe–PGE-oxides and PGE-hydroxides, (5) incorporation of PGE into ferruginous supergene products and lastly (6) concentration of PGE at the edges of veins and iron oxides. Dispersion of Pd is greater than for the other PGE with Pd being widely distributed throughout the iron oxides. This oxidising environment produced PGE-oxides rather than PGE-alloys, also commonly found in the surface environment, especially in placers. These results provide critical evidence for the stages of mineralogical change from PGE host mineralogy in magmatic ores to surface weathering producing PGE-oxides.     

Soil macroporosity and infiltration characteristics of a forest podzol

Spatial distribution of soil macroporosity was determined for a forest podzol from tension infiltrometer measurements at the soil surface. Surface‐derived macroporosity values were compared with point infiltration characteristics obtained from soil water content and soil water chemistry measurements during an experimental irrigation, and with parameters of a kinematic wave model applied to soil water content data. Macroporosity estimated by the tension infiltrometer ranged from 0·00087 to 0·0219% of soil volume, and infiltration at these two sites was dominated by propagation of a well‐defined wetting front through the soil profile and bypass flow via soil macropores, respectively. Infiltration at sites with intermediate macroporosities reflected a combination of these two processes, although results were inconclusive at one site owing to lateral flow at the base of the soil profile. There was no agreement between macroporosities estimated by the tension infiltrometer and the kinematic wave model. The maximum soil conductance parameter within the profile at a site, however, was related directly to the surface‐derived macroporosity. The partial agreement between surface‐derived macroporosity estimates and point infiltration characteristics shown here supports the use of tension infiltrometry as a rapid, non‐destructive method of assessing spatial variations in the relative contribution of macropore flow to the infiltration process. Copyright © 2000 John Wiley & Sons, Ltd.     

Observations of gravity waves in the upper and lower stratosphere by lidar and ozonesondes

Lidar observations of Rayleigh backscatter and temperature profiles measured by ozonesondes have been used to investigate gravity waves in the upper and lower stratosphere, respectively, over Aberystwyth (52.4°N, 4.1°W). Both data sets have been used to investigate the vertical wavenumber spectrum of the wave field at high wavenumbers. Similar analytic techniques applied to each data set enable direct comparison of the spectra. The possibility of laminar structures generated by differential advection contaminating gravity-wave fields deduced from temperature and/or density measurement is discussed and the behaviour of the wave-field mean potential energy reveals a seasonal cycle throughout the stratosphere with a late winter maximum and a summer minimum.     

Magnetic polarity stratigraphy of the Mio-Pliocene mammal-bearing Big Sandy Formation of western Arizona

The Big Sandy Formation in western Arizona consists of up to 65 m of clays, silts, sands and volcanic ashes that were deposited in a lacustrine paleoenvironment. Three paleomagnetic samples were collected from each of 54 sites spaced at stratigraphic intervals of no more than 5 m. After laboratory studies of pilot samples to determine their paleomagnetic characteristics, all other samples were measured for their NRM and then demagnetized in alternating fields of 150 Oe. After statistical filtering and a hierarchical site classification, 48 sites were used to interpret the magnetic polarity zonation.Vertebrate fossils from the Big Sandy Formation are collectively termed the Wikieup Local Fauna, and indicate a late Hemphillian Land Mammal “Age”. Three fission-track (zircon) dates from the Big Sandy Formation yielded a mean age of 5.5 ± 0.2 m.y. B.P. Using these radiometric data to calibrate the magnetic polarity zonation, it appears that the Big Sandy Formation spans late Epoch 6 to early Gilbert time (late Miocene to early Pliocene). The Wikieup Local Fauna is compared to two other roughly contemporaneous mammalian assemblages from New Mexico and Texas. Faunal differences previously thought to represent a very late Hemphillian age for the Wikieup Local Fauna are apparently related to ecogeographic variation and not time.     

Calibration of an estuarine sediment transport model to sediment fluxes as an intermediate step for simulation of geomorphic evolution

Modeling geomorphic evolution in estuaries is necessary to model the fate of legacy contaminants in the bed sediment and the effect of climate change, watershed alterations, sea level rise, construction projects, and restoration efforts. Coupled hydrodynamic and sediment transport models used for this purpose typically are calibrated to water level, currents, and/or suspended-sediment concentrations. However, small errors in these tidal-timescale models can accumulate to cause major errors in geomorphic evolution, which may not be obvious. Here we present an intermediate step towards simulating decadal-timescale geomorphic change: calibration to estimated sediment fluxes (mass/time) at two cross-sections within an estuary. Accurate representation of sediment fluxes gives confidence in representation of sediment supply to and from the estuary during those periods. Several years of sediment flux data are available for the landward and seaward boundaries of Suisun Bay, California, the landward-most embayment of San Francisco Bay. Sediment flux observations suggest that episodic freshwater flows export sediment from Suisun Bay, while gravitational circulation during the dry season imports sediment from seaward sources. The Regional Oceanic Modeling System (ROMS), a three-dimensional coupled hydrodynamic/sediment transport model, was adapted for Suisun Bay, for the purposes of hindcasting 19th and 20th century bathymetric change, and simulating geomorphic response to sea level rise and climatic variability in the 21st century. The sediment transport parameters were calibrated using the sediment flux data from 1997 (a relatively wet year) and 2004 (a relatively dry year). The remaining years of data (1998, 2002, 2003) were used for validation. The model represents the inter-annual and annual sediment flux variability, while net sediment import/export is accurately modeled for three of the five years. The use of sediment flux data for calibrating an estuarine geomorphic model guarantees that modeled geomorphic evolution will not exceed the actual supply of sediment from the watershed and seaward sources during the calibration period. Decadal trends in sediment supply (and therefore fluxes) can accumulate to alter decadal geomorphic change. Therefore, simulations of future geomorphic evolution are bolstered by this intermediate calibration step.     

Late Quaternary palaeohydrology of the Konya Basin, Turkey, based on isotope studies of modern hydrology and lacustrine carbonates

The Konya plain in south central Anatolia, Turkey, which is now largely dry, was occupied around the time of the Last Glacial Maximum by a fresh-oligosaline lake covering more than 4000 km². Sediment cores from three residual water bodies (Pinarbai, Akgöl and Süleymanhaci) within the larger Pleistocene lake basin, have been analysed using a multidisciplinary approach. The sediment sequences are dated as spanning the last 50 Ka years, although breaks in sedimentation mean that there is only partial chronological overlap between them. Carbon and oxygen isotope analyses on lacustrine carbonate from the three cores give contrasting isotope profiles which reflect the different ages and independent hydrological behaviour of different sub-basins through the late Quaternary. Distinguishing changes that are regional from local effects is aided by modern isotope hydrology studies and by comparing the carbonate ¹³C and ¹⁸O values to diatom and other analyses undertaken on the same cores.     

Visible and infrared photometry of Kuiper Belt objects: searching for evidence of trends

We present new visible-infrared (V−J) observations of 17 Kuiper Belt objects, of which 14 were observed in the visible and infrared wavebands simultaneously to limit the effects of lightcurve variations. Combining these data with our previously published visible-infrared data provides a dataset of 29 objects, 25 of which offer simultaneous V−J colors. We examine the resulting dataset for evidence of relationships between physical properties and orbital characteristics. We find no evidence of a color-size relationship (as previously suspected), at least over the size range sampled. The dataset supports the trend, reported elsewhere, that there is a predominance of red material on the surfaces of objects having perihelia beyond 40 AU. Our data are also supportive, albeit weakly, of a reported correlation between inclination and color in the classical Kuiper Belt — although it is perhaps more correct to say that our data show that there appears to be a lack of low inclination blue objects. Our V−J colors appear broadly correlated with published optical colors, thus suggesting that the surfaces of Kuiper Belt objects are subject to a single reddening agent.