A comparative simulation study of coupled THM processes and their effect on fractured rock permeability around nuclear waste repositories

This paper presents an international, multiple-code, simulation study of coupled thermal, hydrological, and mechanical (THM) processes and their effect on permeability and fluid flow in fractured rock around heated underground nuclear waste emplacement drifts. Simulations were conducted considering two types of repository settings (1) open emplacement drifts in relatively shallow unsaturated volcanic rock, and (2) backfilled emplacement drifts in deeper saturated crystalline rock. The results showed that for the two assumed repository settings, the dominant mechanism of changes in rock permeability was thermal–mechanically induced closure (reduced aperture) of vertical fractures, caused by thermal stress resulting from repository-wide heating of the rock mass. The magnitude of thermal–mechanically induced changes in permeability was more substantial in the case of an emplacement drift located in a relatively shallow, low-stress environment where the rock is more compliant, allowing more substantial fracture closure during thermal stressing. However, in both of the assumed repository settings in this study, the thermal–mechanically induced changes in permeability caused relatively small changes in the flow field, with most changes occurring in the vicinity of the emplacement drifts.     

Hybrid analytical and finite element numerical modeling of mass and heat transport in fractured rocks with matrix diffusion

Quantification of mass and heat transport in fractured porous rocks is important to areas such as contaminant transport, storage and release in fractured rock aquifers, the migration and sorption of radioactive nuclides from waste depositories, and the characterization of engineered heat exchangers in the context of enhanced geothermal systems. The large difference between flow and transport characteristics in fractures and in the surrounding matrix rock means models of such systems are forced to make a number of simplifications. Analytical approaches assume a homogeneous system, numerical approaches address the scale at which a process is operating, but may lose individual important processes due to averaging considerations. Numerical stability criteria limit the contrasts possible in defining material properties. Here, a hybrid analytical–numerical method for transport modeling in fractured media is presented. This method combines a numerical model for flow and transport in a heterogeneous fracture and an analytical solution for matrix diffusion. By linking the two types of model, the advantages of both methods can be combined. The methodology as well as the mathematical background are developed, verified for simple geometries, and applied to fractures representing experimental field conditions in the Grimsel rock laboratory.     

ESR Dating of the Evolution of the Shuanghu Basin in the Northern Tibetan Plateau

The Shuanghu basin is a NE-trending rift basin bounded by NE-striking normal faults and NW-striking shear-extensional faults of the northern Tibetan Plateau. Four samples from calcite veins in marginal faults and one sample from mudstone (S-3) were collected for dating the evolution of the Shuanghu basin by using the ESR spectrograph of EXM-type. Ages were calculated according to the close-equilibrium model on the basis of the measured ESR signal spectra of samples, providing good chronological information. It is known from the ESR dating that the extensional faulting and rifting of the Shuanghu area began at 4.92 Ma B.P., followed by regional folding in 3.56-1.36 Ma, NW-striking faulting in 0.60 Ma and normal faulting in 0.024 Ma in the Shuanghu basin.     

Insect communities of Phragmites habitats used for sewage purification: Effects of age and area of habitats on species richness and herbivore-parasitoid interactions

In 1994, 28 sewage purification plants based on common reed Phragmites australis were analyzed, to study fragmentation effects on diversity and on food web structure of insect communities. Purification plants differed in age (2 to 11 years) and area (10 to 2,500 m²). Both age and area were significantly correlated with species richness of herbivores. Populations of the two most abundant herbivores, the gall makers Lipara pullitarsis (Diptera, Chloropidae) and Giraudiella inclusa (Diptera, Cecidomyiidae), increased significantly with age and size of the Phragmites habitats, i.e. the purification plants. Incidence curves showed that only habitats older than 6 years and larger than 100 m² have a 50% probability of finding these two most abundant gall makers, and can correspondingly be considered to contribute to insect species conservation. Natural enemies were even more susceptible to habitat fragmentation than their phytophagous hosts or prey, thereby hampering possible biocontrol. Percent parasitism of both the Lipara and Giraudiella gall makers significantly increased with habitat age.     

Gamma rays from colliding winds of massive stars

Colliding winds of massive binaries have long been considered as potential sites of non-thermal high-energy photon production. This is motivated by the detection of non-thermal spectra in the radio band, as well as by correlation studies of yet unidentified EGRET γ-ray sources with source populations appearing in star formation regions. This work re-considers the basic radiative processes and its properties that lead to high energy photon production in long-period massive star systems. We show that Klein–Nishina effects as well as the anisotropic nature of the inverse Compton scattering, the dominating leptonic emission process, likely yield spectral and variability signatures in the γ-ray domain at or above the sensitivity of current or upcoming gamma ray instruments like GLAST-LAT. In addition to all relevant radiative losses, we include propagation (such as convection in the stellar wind) as well as photon absorption effects, which a priori can not be neglected. The calculations are applied to WR 140 and WR 147, and predictions for their detectability in the γ-ray regime are provided. Physically similar specimen of their kind like WR 146, WR 137, WR 138, WR 112 and WR 125 may be regarded as candidate sources at GeV energies for near-future γ-ray experiments. Finally, we discuss several aspects relevant for eventually identifying this source class as a γ-ray emitting population. Thereby we utilize our findings on the expected radiative behavior of typical colliding wind binaries in the γ-ray regime as well as its expected spatial distribution on the γ-ray sky.     

High-pressure synthesis,long-term stability of single crystals of diboron trioxide,B<Subscript>2</Subscript>O<Subscript>3</Subscript>, and an empirical electronic polarizability of <Superscript>[3]</Superscript>B<Superscript>3+</Superscript>

Single crystals of B₂O₃ are needed for the precise determination of the refractive indices used to calculate the electronic polarizability α of 3-coordinated boron. The α(B) values in turn are used to predict mean refractive indices of borate minerals. Since the contribution of boron to the total polarizability of a mineral is very low, the synthetic compound B₂O₃ represents an ideal model system because of its high molar content of boron. Millimeter-sized crystals were synthesized at 1 GPa in a piston-cylinder apparatus. The samples were heated above the liquidus (800 °C), subsequently cooled at 15 °C/h to 500 °C and finally quenched. The refractive indices were determined by the immersion method using a microrefractometer spindle stage. The refractive indices n _o = 1.653 (3) and n _e = 1.632 (3) correspond to a total polarizability for B₂O₃ of α = 4.877 Å³. These values were used to determine the electronic polarizability of boron of α(B) = 0.16 Å³. Although the surface of the B₂O₃ crystals was coated with a hydrous film immediately after being exposed to air, its bulk crystallinity is retained for a period of at least 2 months.     

Use of a parsimonious rainfall–run‐off model for predicting hydrological response in ungauged basins

A new parameter parsimonious rainfall–run‐off model, the Distance Distribution Dynamics (DDD) model, is used to simulate hydrological time series at ungauged sites in the Lygne basin in Norway. The model parameters were estimated as functions of catchment characteristics determined by geographical information system. The multiple regression equations relating catchment characteristics and model parameters were trained from 84 calibrated catchments located all over Norway, and all model parameters showed significant correlations with catchment characteristics. The significant correlation coefficients (with p‐value < 0.05) ranged from 0.22 to 0.55. The suitability of DDD for predictions in ungauged basins was tested for 17 catchments not used to estimate the multiple regression equations. For ten of the 17 catchments, deviations in Nash–Sutcliffe efficiency (NSE) criteria between the calibrated and regionalised model were less than 0.1, and for two calibrated catchments within the Lygne basin, the deviations were less than 0.08. The median NSE for the regionalized DDD for the 17 catchments for two time series was 0.66 and 0.72. Deviations in NSE between calibrated and regionalised models are well explained by the deviations between calibrated and regressed parameters describing spatial snow distribution and snowmelt respectively. The quality of the simulated run‐off series for the ungauged sites in the Lygne basin was assessed by comparing flow indices describing high, medium and low flow estimated from observed run‐off at the 17 catchments and for the simulated run‐off series. The indices estimated for the simulated series were generally well within the ranges defined by the 17 observed series. Copyright © 2014 John Wiley & Sons, Ltd.