Antero Lindberg

Study of porosity and migration pathways in crystalline rock by impregnation with 14C-polymethylmethacrylate

Abstract A new method is described, which gives quantitative information on levels and spatial distributions of porosity in the matrix of rock in the sub-mm- to cm-scale. Migration pathways can be identified and visualized. The method employs impregnation of dried rock samples by 14 C-labelled methylmethacrylate (MMA), radiation polymerization, autoradiography and digital image processing. Infiltration and diffusion processes can be quenched by polymerization and the resulting profiles studied easily.

The effect of microscale pore structure on matrix diffusion—a site-specific study on tonalite

The matrix diffusion of non-sorbing tracers was studied in rocks from the Syyry area, Central Finland (SY1). The effect of alteration and weathering on rock matrix porosity and on the available pore space, which affects diffusivity, are discussed. The main rock type in the crystalline bedrock of Syyry is a slightly foliated, gray tonalite with mica gneiss inclusions as well as minor, more mafic inclusions. The total porosity and the spatial porosity distribution and microstructure of the rocks were investigated using infiltration of carbon- 14-methylmethacrylate, electron microscopy and Hg-porosimetry. The laboratory-scale diffusion experiments were performed using (1) the out-leaching technique of methylmethacrylate (MMA), (2) the through-diffusion of tritiated water (HTO) and chloride in the liquid phase and (3) the through-diffusion of helium in the gas phase. The results of structure investigations indicate that alteration and weathering create micrometric-scale pore apertures, visible as fissures and cracks. These migration pathways dominate in laboratory-scale diffusion experiments and result in high effective porosities and effective diffusivities. Alteration also creates spherical pores, smaller than 1 μm, especially in heavily altered biotite and plagioclase minerals. The altered mineral phases act as quasi dead-end pores hindering the diffusion of non-sorbing tracers. The heterogeneity of the matrix is increased. The heterogeneous spatial pore structure of altered and weathered rock samples causes uncertainty in the diffusion coefficients owing to an assumed homogeneous matrix in Fickian diffusion models.

Radionuclide transport and retardation in rock fracture and crushed rock column experiments

Transport and retardation of non-sorbing tritiated water and chloride and slightly sorbing sodium was studied in Syyry area SY-KR7 mica gneiss, in altered porous tonalite and in fresh tonalite. Experiments were performed using dynamic fracture and crushed rock column methods. Static batch method for sodium was introduced to compare retardation values from static and dynamic experiments. The 14C-PMMA method was used to study the pore structure of matrices. The pore aperture distribution was evaluated from Hg-porosimetry determinations and the surface areas were determined using the B.E.T. method. The flow characteristics and transport behavior of tracers were interpreted using a numerical compartment model for dispersion. The effect of matrix diffusion was calculated using an analytical solution to the advection-matrix diffusion problem in which surface retardation was taken into account. Radionuclide transport behavior in rock fractures was explained on the basis of rock structure.

The Distribution of Natural Radionuclides on Fracture Surfaces in Palmottu Analogue Study Site in SW Finland

The distribution of U and Th on fracture surfaces near an uranium ore deposit was studied by the selective dissolution technique. Uranium series disequilibrium measurements and the analysis of Ca, Mg, Fe and Μη were used to interpret radiogeochemical phenomena and mechanisms which have been responsible for the observed radionuclide distribution in the study site. The principal minerals identified in fracture coatings were in varying proportions kaolinite, calcite, quartz and illite. The bulk of the thorium and uranium was found in the carbonate phase. The isotopic distribution indicates uranium sorption in different groundwater conditions and recent rockgroundwater interaction. The activity ratio of uranium and thorium isotopes in calcite were also used to estimate the depositional age of the calcite. The average ages for the two calcites were 80000 years and 300000 years or older.

Modeling of cesium sorption on biotite using cation exchange selectivity coefficients

Abstract For the modeling of cesium sorption on biotite, samples of natural biotite separated from gneissic rocks were converted into monoionic potassium, sodium, and calcium forms, and sorption isotherms for Cs/K, Cs/Na and Cs/Ca exchange were determined at pH 6 and 8 in E-4–E-8 M Cs solutions. Selectivity coefficients for Cs/K, Cs/Na, and Cs/Ca ion exchange reactions were calculated from the isotherm data, using the Gaines-Thomas convention. At Cs loadings below 1% of the total ion exchange capacity, the overall selectivity coefficient for Cs/Ca exchange was approximately five and seven orders of magnitude higher than those for Cs/Na and Cs/K exchange, respectively. Based on the selectivity coefficients, the ion exchange isotherms were modeled with the U.S. Geological Survey PhreeqC program, assuming three different types of ion exchange site: sites on the basal planes on biotite crystal surfaces with 95% site abundance, probable interlayer sites on crystal edges [frayed edge sites (FESs)] (0.02%) and third-type sites (5%), the physical background of which is unclear. Of these three types, the FES sites were superior in Cs selectivity, while the planar sites exhibited the lowest selectivity, and the third-type sites had selectivity between these two. The functionality of the model was successfully verified by modeling the Cs sorption isotherms on crushed mica gneiss rock in saline groundwater. Determination of the exchangeable ions K, Na, Ca, and Cs on the basal plane and edge surfaces by scanning electron microscopy-energy-dispersive x-ray spectroscopy (SEM-EDX) supports the results of modeling: edge sites highly prefer Cs ions and also Ca and Na ions but not K ions.

Detection of irradiated foods by luminescence of contaminating minerals—effect of mineral composition on luminescence intensity

Laboratory irradiated rock and mineral samples were studied for their luminescence properties. The effect of alteration of feldspars on luminescence intensity was determined by the autoradiographic method for porphyritic granodiorite planar rock samples and with the TL reader for crushed minerals. Feldspars and quartz exhibited more intensive luminescence than mafic minerals, and luminescence of fresh K feldspar was the most intense. Potassium concentration did not have any effect on luminescence intensity for K feldspars but the intensity was highly dependent on the alteration degree of the mineral. Decrease in luminescence was found without a change in the element composition of the mineral and alteration was due to sericitization of K feldspar.

Effect of feldspar composition on thermoluminescence in minerals separated from food

Abstract Study was made of factors influencing the thermoluminescence (TL) intensity of feldspars separated from irradiated foods. Autoradiography and optical densitometry with application of digital image processing was found to be a suitable method for determining the mineral specific differences in irradiated feldspars. Alteration of K feldspar was observed to reduce the luminescence intensity. A structural change from unaltered mineral to fully seriticized form without marked change in element composition was accompanied by a decrease in TL from very intensive to nonobservable. Likewise increase in FeO concentration during alteration was accompanied by decrease in the TL intensity. Thermoluminescence of plagioclase increased with the CaO/Na 2 O ratio.

Effect of mineral composition on thermoluminescence detection of irradiated seafood

Abstract Data from import control of irradiated seafood were collected from 300 batches of seafood. Thermoluminescence (TL) analysis of the seafood, based on measurement of thermoluminescent minerals separated from intestinal tract, was carried out with a Riso TL-DA-10 instrument. As identified by X-ray diffraction and SEM/EDS analysis, four main categories of minerals were extracted: tectosilicates, phyllosilicates, carbonates and sulphates. Detection of irradiation was reliable when based on the TL of tectosilicate minerals, i.e. quartz and feldspar. Suitable minerals were found in most seafood: only about five percent of all samples could not be successfully analysed because no minerals or only non-thermoluminescent clays or carbonates were found. False positive results were never obtained. A false negative decision results if analyses are based on hydrous clays or carbonates in the form of aragonite.

Multi-scale study of the mineral porosity of veined gneiss and pegmatitic granite from Olkiluoto, Western Finland

The purpose of this work was to support the long-term experiments for investigation of rock matrix retention properties at the spent nuclear fuel repository site ONKALO, in Olkiluoto, Western Finland. Towards this end, rock samples were characterised in terms of porosity connected to mineralogy, with emphasis on pore sizes, and fillings. Both filled and unfilled pores were found with unfilled pores being majority in the pegmatitic granite veins of the mostly veined gneiss samples. It was found that the fillings were often connected to local alteration and the alteration caused variation in the range of pore sizes.

Na, Ca and Sr Retardation on Crushed Crystalline Rock

Different approaches for measuring the interaction between radionuclides and rock matrix are needed to test the compatibility of transport models and retardation experiments. In this work sorption of sodium (Na), calcium (Ca) and strontium (Sr) was studied on mica gneiss, unaltered, moderately altered and strongly altered tonalite samples taken from hole SY-KR7 drilled in the Syyry area in Sievi in western Finland. The mass distribution ratio values for sieved fractions were determined using static batch and thin section methods as well as crushed rock column method. Sodium, calcium and strontium sorption on mica gneiss and unaltered tonalite was slight and no difference due to fraction size was observed. Higher sorption and fair dependence on fraction size was obtained for altered tonalites owing to the composition of alteration minerals and larger specific surface areas. Difference in the Rd values between unaltered and altered rocks is partly the result of the higher specific surface areas for altered rocks, /{^-values calculated from thin section /{„-values and Rjvalues obtained from batch experiments were in good agreement. Except for sodium, Rvalues obtained from column experiments were lower but in agreement with Rvalues from batch and thin section experiments.