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11.
Performance assessment of deep repositories for heat-generating radioactive waste requires the capability of predicting reliably the evolution of the system during a time period commensurate with the hazardous life of the waste. In many repository designs clay barriers represent important elements of the waste isolation system.
In order to provide reasonable assurance that clay barriers will ensure long-term waste isolation, it is essential to understand their behaviour under a variety of conditions. Due to the variability of argillaceous materials, to the complexity of the phenomena that might take place in a waste repository and to the longevity of the required isolation, an adequate understanding of the behaviour and the capability to model the evolution of the clay barriers are not easy tasks. The factors that need to be understood and modelled include stress evolution, long-term strain or creep, thermal effects on solid skeleton, on interstitial fluids and on mineralogy. The difficulty of the task is increased by the facts that many effects are coupled, that their rates must be extremely low, in order to be realistic, and that the time period to be modelled defies the possibility of direct experimental observation. Several critical issues are identified and discussed briefly, such as: constitutive law to describe the thermo-mechanical behaviour of the clay skeleton, modelling of the fluid phase in clays and its response to heating, thermal fracturing and healing. Strategies are suggested for a rational approach to the experimental investigation of some relevant processes. The study of suitable natural analogues, for example the thermo-metamorphic halo occurring at Orciatico in Tuscany, could provide valuable insights in the thermal effects of heating clay barriers. It is conceivable that models describing a variety of relevant phenomena, such as dehydration, fracturing and permeability changes could be tested through the study of the Orciatico analogue.
In the end performance assessments of clay barriers would benefit through improvements in modelling: this would involve progress in understanding the basic phenomena and their coupled nature, improved conceptual and mathematical models and increased reliability for their calibration/validation. The improved understanding of phenomena requires additional experimental activities on various levels: molecular, microscopic, macroscopic, medium scale and in situ. 相似文献
12.
Ramesh K. Kapoor B. B. Adiga S. P. Singal S. K. Aggarwal B. S. Gera 《Boundary-Layer Meteorology》1982,24(4):415-419
Observations made with a monostatic sodar and from a 120 m instrumented tower have been used to study the variations in the atmospheric boundary layer at Tarapur (19° 50 N, 72° 41 E) during the solar eclipse of February 16, 1980. Atmospheric instability was reduced below normal values during the eclipse but the atmosphere at no time became stable. 相似文献
13.
P. K. Pasricha B. S. Gera S. Shastri H. K. Maini T. John A. B. Ghosh M. K. Tiwari S. C. Garg 《Boundary-Layer Meteorology》2003,107(2):469-482
Nocturnal measurements of air temperature, relative humidity, temperatureinversion-layer thickness, water vapour path and visibility-through-fog, madeunder non-foggy and foggy conditions in winter over two seasons at Delhi,are analysed to study the decrease in both rate of cooling and temperature inversion-layer thickness during the course of nights followed by fog occurrence.In particular, the decrease in the rate of cooling, compared to that on non-foggynights, is explained as due to the greenhouse warming effect by a layer of excessive,near-saturated water vapour trapped in a temperature inversion. Next, the linearprogramming technique is employed to forecast the occurrence of fog, where thevisibility-through-fog is minimized through its linear regression equation with thepair of variables, mean air temperature and temperature decrease over one hour(measuring rate of cooling at two convenient hours) in the pre-midnight period.This technique provides feasible solutions that enables one to forecast the occurrenceof radiative fog. 相似文献
14.
Tomas A. Tam III Graciano P. Yumul Jr Estephanie Gera L. Ramos Carla B. Dimalanta Mei-Fu Zhou Shigeyuki Suzuki 《Resource Geology》2005,55(3):217-224
Abstract. Petrographic analysis of the Oligocene-Miocene Zigzag Formation and Miocene Klondyke Formation of the Baguio Mineral District reveals a transitional arc source for the former and an undissected arc source for the latter. Whole rock geochemistry of these sedimentary rock formations show affiliation of the Zigzag Formation to active continental margin whereas the Klondyke Formation appears to have been derived from an oceanic island arc source. A different aspect of the geology of the district is further gleaned from the whole rock rare earth element geochemistry of these rocks. Samples from the Zigzag Formation are characterized by higher REE concentrations compared to the Klondyke Formation samples. The REE data indicate that the sedimentary rocks of the Klondyke Formation had geochemically-less fractionated igneous lithologies as their progenitor whereas the older Zigzag Formation was derived from a more differentiated source. This new set of information contributes to the understanding of the evolution of this district from a marginal basin to an island arc setting. 相似文献
15.
B. S. Gera S. P. Singal Neeraj Saxena Y. S. Ramakrishna 《Journal of Earth System Science》1996,105(3):261-272
A monostatic sodar was set up at Jodhpur, near the western end of the monsoon trough, to investigate the atmospheric boundary
layer dynamics. A 30 m instrumented tower was also located close to the sodar antenna. Data were collected from June to August
during the monsoon period of 1990, as also from July 1992 to September 1993.
Thermal plumes, surface-based stable layers (both flat or short spiky top and tall spiky top), elevated/multi-layers with
or without undulations and dot echo structures were seen; however, erosion of the morning inversion layer in the form of a
rising layer with growing thermal plumes under it was rarely seen, and that too only during the winter period. The observed
structure of the stable layer with tall spikes and its depth have been found to be correlated with the intensity of the monsoon
spell; the dot echoes have been found to be correlated with the approach of a monsoon depression near Jodhpur; and the elevated/multilayers
have been attributed to the formation of a subsidence (shear instability). 相似文献
16.
Shear echoes with various types of structures like surface layer with smooth top, short spiky top, tall spiky top and stratified layers have been seen on the monostatic system operating at the National Physical Laboratory, New Delhi. In this paper effects of surface wind speed on the formation of these structures have been considered. The data used for the purpose pertains to the period May 1977 to April 1982. It has been seen that most of the shear echo structures are formed under stable conditions with surface wind speed less than or equal to 2.5 m s−1, however, the tall spiky surface based layer structures of height more than 150 m have been seen to occur significantly in the presence of higher surface wind speeds, suggesting that strong surface winds may be responsible for turbulence in the vertical plane to more depth. 相似文献
17.
Graciano P. Yumul Jr Carla B. Dimalanta Tomas A. Tam III Estephanie Gera L. Ramos 《Island Arc》2008,17(4):432-442
The Baguio Mineral District exposes rock formations that evince the geological and tectonic evolution of this district from a subduction‐related marginal basin to an island arc setting. Available onshore and offshore data are consistent with an Early (onset phase) to Middle (developed phase) Miocene arc polarity reversal from the east (termination of subduction along the proto‐East Luzon Trough) to the west (initiation of subduction along the Manila Trench). Geophysical modeling and geochemical data calculation showed a 30 ± 5 km crustal thickness for the mineral district. Subduction‐related multiple arc magmatism and ophiolite accretion contributed to crustal thickening. Recent information on the Oligo–Miocene Zigzag and Klondyke formations in the mineral district reveal that the marginal basin, where these rocks were deposited, has received eroded materials from adjacent terrains characterized by siliceous lithologies. Furthermore, adakitic rocks, high permeable zones and extensional zones which are exploration markers applied to identify possible mineralization targets, are prevalent in the mineral district. The geological evolution that the district had undergone mimics the evolution of island arcs worldwide in general and northern Luzon in particular. 相似文献
18.
G. Rajkumar R. Narasimha S. P. Singal B. S. Gera 《Journal of Earth System Science》1996,105(3):325-341
Radiosonde data from Jodhpur, taken at 0530, 1730 and around 1100 hr IST during MONTBLEX 1990, reveal that the distribution
of virtual potential temperature0
v below about 500 hPa has a structure characterized by up to three layers each of approximately constant gradient. We are thus
led to introduce a characterization of the observed thermal structure through a sequence of the symbolsN, S andU, standing respectively for neutral, stable or unstable conditions in the different layers, beginning with the one closest
to the ground. It is found that, of the 29 combinations possible, only the seven classes,S, SS′, SNS′, NS, NSS′, USS′ andUNS are observed, whereS′ stands for a stable layer with a different gradient of0
r. than in the layerS. It is also found that, in 90% of the launches at 0530 hr, 48% of the launches at 1730 hr and 69% of the launches around
1100 hr, the first radiosonde layer near the ground is stable; the classical mixed layer was found in only 11 % of the data
set analysed, and, if present on other occasions, must have been less than 250 m in height, the first level at which radiosonde
data are available. Supplementing the above data, sodar echograms, available during 82% of the time between June and August
1990, suggest a stable layer up to a few tens of metres 48% of the time. A comparative study of the radiosonde data at Ranchi
shows that the frequent prevalence of stability near the surface at Jodhpur cannot be attributed entirely to the large scale
subsidence known to be characteristic of the Rajasthan area. Further, data at Jodhpur reveal a weak low level jet at heights
generally ranging from 400 to 900 m with wind speeds of 6 to 15 m/s. Based on these results, it is conjectured that the lowest
layers in the atmosphere during the monsoons, especially with heavy clouding or rain, may frequently be closer to the classical
nocturnal boundary layer than to the standard convective mixed layer, although often with shallow plumes that penetrate such
a stable layer during daytime. 相似文献
19.
This study analyzes the vegetative and soil degradation, measured as biomass and soil loss, for Arnigad micro-watershed located
in Indian Himalayan state of Uttarakhand, in systems framework by using dynamic linear programming bio-economic model. The
focus is at investigating the effects of alternate policy regimes, i.e., introduction of improved energy sources for cooking
along with substitution of existing local livestock breeds with improved breed, reduction in human population growth and introduction
of high yielding varieties of main crops including paddy, maize and wheat. The model horizon extended over a period of 25
years, i.e., from 2006 to 2030. It was found that the model scenario incorporating increased use of improved energy sources
along with substitution of local cows by improved cows could be the most effective policy option in reducing vegetative and
soil degradation. The vegetative biomass density declined to 19.76% compared to 35.24% in the BASE scenario and soil erosion
loss was also lowered by 29.13%. Also, the reduction of population growth rate to half of the BASE scenario led to minor improvements
in degradation. Introduction of high yielding varieties of main crops slightly increased vegetative degradation but reduced
soil loss (8.35%) with respect to the BASE scenario. Such a phenomenon could be explained in terms of changed crop mix resulting
in reduced amount of crop by-products requiring increased lopping of tree branches for animal fodder. The policy option of
the increased use of improved energy sources along with substitution of improved breed of cows resulted in 9.58% higher income.
Introduction of high yielding varieties of crops led to 1.92% increase in income, but the income decreased by 1.25 % when
population growth was reduced to half. The usefulness of the model lies in analyzing the systems behavior in its entirety
where the results can predict the possible direction of change as a result of manipulation in alternate economic regimes. 相似文献
20.
Measured concentration levels of carbon monoxide present in the atmosphere near the ground surface have been studied in relation to atmospheric stability inferred from acoustic sounder vis-à-vis the density of motor-vehicular traffic responsible for the emission of carbon monoxide gas. It has been seen that concentration levels of carbon monoxide during peak traffic hours depend on the prevailing stability of the atmosphere. The need for continuous monitoring of atmospheric stability at a place using acoustic sounder to assess air quality has been emphasized. 相似文献