Rock matrix diffusivity determinations by in-situ electrical conductivity measurements

A fast method to determine rock matrix diffusion properties directly in the bedrock would be valuable in the investigation of a possible site for disposal of nuclear waste. An "effective diffusivity borehole log" would provide important information on the variability of this entity over the area studied. As opposed to traditional matrix diffusion laboratory experiments, electrical conductivity measurements are fast, inexpensive and also easy to carry out in-situ. In this study, electrical resistivity data from borehole logging, as well as from measurements on the actual core, is evaluated with the purpose of extracting matrix diffusivity data. The influence of migration of ions in the electrical double layer, which can be of great importance in low ionic strength pore water, is also considered in evaluating the in-situ data to accurately determine the effective pore diffusivity. The in-situ data compare fairly well to those measured in the rock core.     

Predicting CO2 and SO2 emissions in the Baltic States through reorganization of energy infrastructure

The paper deals with predicting carbon dioxide and sulphur dioxide emissions generated by power production sector in the Baltic States in period up to year 2020. The economies of Lithuania, Latvia and Estonia are rapidly growing therefore forecast of emissions related with this occurrence becomes very important. The Ignalina Nuclear Power Plant (INPP), one of the largest in the world, is situated in the region. Two power production scenarios are modelled to investigate changes in power sector's emissions expected as the consequences of the coming closure of Ignalina NPP. Power market was assumed to be common for all three Baltic countries and was modelled by applying the Balmorel model. The planned closure of Ignalina NPP will bring restructuring of Lithuania power production sector and will change also power transmission between countries. Predictive identified the potential of investments for new modern power generation technologies. At the same time, modelling results show in both scenarios that CO(2) and SO(2) emissions from power production in the Baltic region will increase. The increment of emissions is discussed in the context of meeting requirements of UNFCCC Kyoto protocol and EC Directives. Despite of CO(2) emissions increase the Kyoto protocol's requirements may be expected. At the same time, SO(2) formation in Lithuania power sector may exceed the limits of the EU Council Directive 2001/80/EB therefore the additional measures to control SO(2) emissions have to be investigated.     

Determination of sorption properties of intact rock samples: New methods based on electromigration

Two new methods for determining sorption coefficients in large rock samples have been developed. The methods use electromigration as a means to speed up the transport process, allowing for fast equilibration between rock sample and tracer solution. An electrical potential gradient acts as a driving force for transport in addition to the concentration gradient and forces the cations through the rock sample towards the cathode. The electrical potential gradient induces both electromigration and electroosmotic flow with a resulting solute transport that is large compared to diffusive fluxes. In one of the methods, the solute is driven through the sample and collected at the outlet side. In the other, simpler method, the rock sample is equilibrated by circulating the solute through the sample. The equilibration of rock samples, up to 5 cm in length, with an aqueous solution has been accomplished within days to months. Experiments using cesium as a sorbing tracer yield results consistent with considerably more time demanding in-diffusion experiments. These methods give lower distribution coefficients than those obtained using traditional batch experiments with crushed rock.     

Prediction of some in situ tracer tests with sorbing tracers using independent data

Some recent converging tracer tests with sorbing tracers at the Asp? Hard Rock Laboratory in Sweden, the TRUE tests, have been predicted using only laboratory data and hydraulic data from borehole measurements. No model parameters were adjusted to obtain a better fit with the experiments. The independent data were fracture frequency and transmissivity data obtained in the field and laboratory data on sorption and matrix diffusion. Transmissivity measurements in five boreholes in the rock volume containing the region surrounding the injection and collection points show that there is a high frequency of water conducting fractures. Of 162 packed off sections with 0.5 m packer distances, 112 were found to have a transmissivity above the detection limit. The specific flow-wetted surface (FWS) of the rock mass could be estimated from these data. The transmissivities were found to be reasonably well described by a lognormal distribution. Laboratory data on diffusion and sorption properties together with the hydraulic data were used to "predict" the residence time distribution (RTD) of the sorbing tracers. The results were compared with the experimental breakthrough curves. In these experiments, the water residence time is very small compared to the residence time of the sorbing tracers due to their diffusion and sorption within the rock matrix. We thus could neglect the influence of the water residence time in our predictions. Therefore, no information on water residence times or on "dispersion" was needed. The dispersion of the sorbing tracers is caused by the different sorbing tracer residence times in different pathways. The sorbing tracer residence time is determined by the ratio of flowrate to the flow-wetted surface in the different pathways and not by the water residence time. Assuming a three-dimensional flow pattern and using the observed fracture frequency and flowrate distribution, breakthrough curves for three strongly sorbing tracers were predicted. Only the laboratory data, the transmissivity measurements and the pumping flowrate were used in the predictions. No information on the water residence time as obtained by the nonsorbing tracers was used. The predictions were surprisingly accurate.