Jussi Ikonen

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.

Sorption and diffusion of selenium oxyanions in granitic rock

The processes controlling diffusion and sorption of radionuclides have been studied extensively in the laboratory, whereas, only a few in-situ experiments have been carried out in order to study in-situ diffusion over the long-term (several years). This is largely due to the fact that in-situ experiments are typically time consuming and cost intensive, and it is commonly accepted that laboratory scale tests are well-established approaches to characterizing the properties of geological media. In order to assess the relevance of laboratory experiments, the Swiss National Cooperative for Disposal of Radioactive Waste (Nagra) have been conducting extensive experiments in the Underground Rock Laboratory (URL) at the Grimsel Test Site (GTS) in order to study radionuclide transport and retention in-situ. One of the elements used in these experiments is non-radioactive selenium, as an analog for the radiotoxic isotope Se-79, which is present in radioactive waste. In this work, two laboratory through-diffusion experiments using selenium as a tracer were carried out in block (decimeter) scale rock specimens to support one of the ongoing radionuclide transport and retention in-situ experiment at the GTS mentioned above. The though-diffusion tests of selenium were performed under atmospheric conditions in both Kuru grey granite (KGG) and Grimsel granodiorite (GG). The decrease of selenium concentration in an inlet hole drilled into each of the rock samples and the breakthrough of selenium into sampling holes drilled around the inlet were analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The effective diffusion (De) and distribution coefficients (Kd) of selenium were then determined from the changes of selenium concentration in the inlet and sampling holes using a Time-Domain Diffusion (TDD) simulations. In addition, Kd of selenium was measured by batch sorption experiments as a function of pH and Se concentration in atmospheric conditions and nitrogen atmosphere. The speciation of selenium was studied by HPLC-ICP-MS in simulated ground waters of each of the rock types. The Kd of selenium was found to be in the range of (6.2-7.0±2.0)×10(-3)m(3)/kg in crushed rock whereas the Kd obtained from block scale through diffusion experiment varied between (1.5±0.3)×10(-3)m(3)/kg and (1.0±0.6)×10(-4)m(3)/kg. The De of selenium was significantly higher for GG; De=(2.5±1.5)×10(-12)m(2)/s than for KGG; De=(7±2)×10(-13)m(2)/s due to the higher permeability of GG compared with KGG.

Tritium analysis in building dismantling process using digital autoradiography

The aim of our study was to develop a sensitive analytical technique to investigate tritium traces on concrete floor, ceiling and walls of a laboratory under dismantling process. In dismantling process, the behaviour of tritium must be followed very closely and in particular releases to atmosphere and exposure to public must be prevented. The investigations were carried out using liquid scintillation counting (LSC) and digital autoradiography techniques. The LSC investigations were carried out using wipe tests. It was concluded that even though LSC technique provided accurate information on the level of contamination, the loss of exact localisation of contamination spots was considered to be a major disadvantage in this application. The digital autoradiography was shown to provide both quantitative information and localisation of contamination spots. The exposure time on the digital autoradiography films were optimized, the matrix effect and the selectivity of the films were studied using polymethylmethacrylate standards. The studies showed that the digital autoradiography technique can give quantitative results, especially if standards of the investigated material (concrete) are used.

Analysis of 3H, 36Cl, 133Ba, 134Cs and 22Na from synthetic granitic groundwater: an in situ through diffusion experiment at ONKALO

AbstractA method for analyzing 3H, 36Cl, 22Na, 133Ba and 134Cs from simulated groundwater (SGW) samples was introduced. Gamma emitting radionuclides 22Na, 133Ba and 134Cs were measured by using an HPGe-detector. Beta emitting 3H and 36Cl were separated from gamma emitting 22Na, 133Ba and 134Cs. AgCl precipitation was used for the separation of 36Cl from SGW samples with yields of 98 ± 2%. 3H was separated by distillation with recoveries of 97 ± 3%. This method was used for the determination of activity concentrations of 3H, 36Cl, 22Na, 133Ba and 134Cs in SGW samples collected from an in situ through diffusion experiment.