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Radioactive particles often contain very high radioactivity concentrations and are widespread. They pose a potential risk to human health and the environment. Their detection, quantification, and characterization are crucial if we are to understand their impact. Here, we present the use of a real-time autoradiography gaseous detector (using parallel ionization multiplier) to expedite and improve the accuracy of radioactive particle screening in complex environmental samples. First, standard particles were used to assess the detector capabilities (spatial resolution, spectrometry, and artefact contributions), then, we applied the technique to more complex and environmentally relevant samples. The real-time autoradiography technique provides data with a spatial resolution (≲100 µm) suitable for particle analysis in complex samples. Further, it can differentiate between particles predominantly emitting alpha and beta radiation. Here, the technique is applied to radioactive cesium-rich microparticles collected from the Fukushima Daiichi nuclear exclusion zone, showing their accurate detection, and demonstrating the viability of real-time autoradiography in environmental scenarios. Indeed, for more complex samples (radioactive particles in a less radioactive heterogeneous background mix of minerals), the technique permits relatively high selectivity for radioactive particle screening (up to 61.2% success rate) with low false positive percentages (~ 1%). [ABSTRACT FROM AUTHOR]

MX-80 bentonite colloids' effect on radionuclide sorption was studied by batch method and transport in flow using a granitic drill core column and Sr(II) as a radionuclide. Batch-type sorption and desorption experiments were conducted to determine Sr(II)'s distribution coefficients on bentonite colloids and metatexitic gneiss. Molecular modeling assessed the radionuclide's sorption affinity and justified the differences in Sr(II)'s sorption behavior on biotite versus montmorillonite. The distribution coefficients were found to be a hundred times greater for colloids than for granitic rock. Strontium's breakthrough from the column with bentonite colloids was successful without notable retardation on rock minerals. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Diffusive transport of iodine (I) and tritiated water (HTO) in granodiorite is studied in the framework of the long term diffusion project (LTD) at the Grimsel Test Site, Switzerland. In this paper we modelled the tracer profiles measured in a long term (780 days) in situ diffusion test was carried out as part of LTD. The main outcome of the modelling tends to prove that the in situ apparent diffusion coefficients of I and HTO are close to the reference apparent diffusion coefficient determined in the laboratory ( D = 3 × 10 m s). [ABSTRACT FROM AUTHOR]

As part of the long-term diffusion project a 780 days long in situ diffusion experiment was performed at the Grimsel Test Site where several radionuclides and inactive iodine were circulated in the packered interval in granodiorite. This paper presents in situ diffusion profiles for tritiated water and iodine acquired from overcored sections of the circulation interval by out-leaching. [ABSTRACT FROM AUTHOR]

The Finnish plan for the final deposition of nuclear waste is deposition deep in the crystalline bedrock. In the safety case of the final deposition, matrix diffusion, along with sorption, is considered the most important retarding factor for radionuclide transport in the geosphere. We set out to measure matrix diffusion in the gas phase for two 80 cm long drill-core samples from Olkiluoto, Finland. One sample consisted of veined gneiss and the other of pegmatitic granite. The measurements were taken in the laboratory with an advection-diffusion measurement setup that uses nitrogen as the carrier gas and helium as the tracer. The measured breakthrough curve for the veined gneiss sample could be interpreted with a homogeneous mathematical model, and the result for the effective diffusion coefficient ( $$D_{\mathrm{e}}$$ ), $$4.2 \pm 0.9 \times 10^{-10}\,\frac{\mathrm {m}^2}{\mathrm {s}}$$ , agreed with previous results for veined gneiss from through-diffusion experiments in the gas phase. The breakthrough curve for the pegmatitic granite sample required a three-component model because of high variations in the local transport parameters (porosity, diffusion coefficient). The spatial distributions of porosities were characterized with the $$^{14}$$ C-polymethylmethacrylate-autoradiography technique. The result, $$D_{\mathrm{e}} = \left( 32 \pm 7\right) \times 10^{-10}\,\frac{\mathrm {m}^2}{\mathrm {s}}$$ , for the most abundant component was also in accordance with the previous through-diffusion results. Comparison of the two measurements showed that diffusion phenomena can be very sensitive to the microstructure of rock even when macroscopic properties such as porosity remain the same. The retarding effect of matrix diffusion from flow was clearly observed for both samples, and knowledge of the sample structure, rock types, and mineralogy were concluded to be vital in analyzing and interpreting the results. [ABSTRACT FROM AUTHOR]

Radioactive elements (H, Cl, Na, Sr and Ba) was used and measured in one of the in-situ experiments. The separation scheme had to be developed and optimized. Cl was first extracted by silver chloride precipitation and then Sr and Ba were extracted by Sr/Ba carbonate precipitation after which activities of H and Cl were measured by liquid scintillation counting while activities of gamma emitters (Na, Sr and Ba) were measured by gamma spectrometry from the initial solution. In the precipitation, the recoveries of Cl and Sr were 100 % while the recovery of Ba was about 85 %. The detection limit of H was 0.1 Bq g whereas the detection limit of Cl was 0.05 Bq g. [ABSTRACT FROM AUTHOR]

The Finnish plan for final disposal of nuclear waste is an underground repository in crystalline bedrock in Olkiluoto. In the safety analysis of the repository, it is vital to know the transport properties of the bedrock. We set out to investigate these properties by measuring porosities of rock samples with Ar-gas pycnometry and diffusion coefficients and permeabilities of the same samples with a He-gas method. Diffusion of gases is about 10,000 times faster than diffusion of elements in water, and thus the gas methods are practical tools when determining the properties of relatively tight samples. The porosities were 0.44-0.63 % for pegmatitic granite (three samples) and 0.19-2.9 % for veined gneiss (15 samples). The effective diffusion coefficients were $$ 3.2 \times 10^{-9}$$ - $$8.2 \times 10^{-9}\,{\mathrm {m}}^2/{\mathrm {s}} $$ for pegmatitic granite and $$ 5.0 \times 10^{-10}$$ - $$6.7 \times 10^{-9}\,{\mathrm {m}}^2/{\mathrm {s}} $$ for veined gneiss and the permeabilities $$ 5.9\,\times 10^{-19}$$ - $$6.4 \times 10^{-18}\,{\mathrm {m}}^2 $$ and $$ 1.4 \times 10^{-20}$$ - $$8.6 \times 10^{-17}\,{\mathrm {m}}^2 $$ for the same rock types, respectively. We also investigated the dependences of said properties of one another, and found a correlation between effective diffusion coefficient and permeability. [ABSTRACT FROM AUTHOR]

Digital autoradiography (DA) based on phosphor plate imaging was tested for porosity quantification using C-PMMA method, and was compared to the classical film autoradiography (FA) method. Validation was undertaken by characterizing porosity evolution of moraine deposits of Lamarck granodiorite (eastern Sierra Nevada, USA). The connected porosities obtained with FA and DA are comparable to density measurements. Using adapted exposure times, DA is more accurate than FA for analysing large variations of porosity within a given sample, and is faster than FA. [ABSTRACT FROM AUTHOR]

In the framework of dismantling of nuclear facilities, there is a strong need to obtain analytical results on residual radioactivity especially on concrete but also on metal surfaces. Since investigation of hundreds of m areas by the standard Wipe test method is difficult, a semi quantitative digital autoradiography (DA) technique was developed. The DA technique is sensitive to all types of radiation and therefore it is advantageous in dismantling investigations. Recent developments on the DA technique were investigated on concrete floor of an old laboratory in which research had been carried out using H and C beta emitters. The results showed that the DA technique was a powerful tool in localization and quantification of residual radioactivity on concrete floor. [ABSTRACT FROM AUTHOR]

Spent nuclear fuel repository safety evaluation today requires both laboratory and in situ field work in order to assess the parameters affecting the sorption and diffusion of radionuclides. Recent investigations at the Grimsel test site suggest that non-conservative errors in transport properties derived from laboratory scale experiments can lead to over-conservative estimates of matrix diffusion depths. As a result, the geosphere's capability to retain radionuclides may be underestimated. In this study the in situ diffusion and the sorption of Cs and Na into granodiorite were determined using gamma spectroscopy. Autoradiography was used to reveal the minerals into which the radionuclides were sorbed. A rock sample was obtained from the Grimsel underground in situ diffusion test site in Switzerland. In the in situ test, a solution containing several different radionuclides was circulated continuously in a packed-off injection hole for two years and three months in order to study diffusion of the radionuclides into the surrounding bedrock. The gamma measurements show that in the course of the experiment Cs diffused 2.5 cm and Na 10 cm into the rock matrix, respectively. Caesium was found to have sorbed on mafic minerals biotite and chlorite. Results of this study were used in order to calculate an in situ effective diffusion coefficient for caesium and sodium in Grimsel granodiorite. [ABSTRACT FROM AUTHOR]

Numerical time-domain-diffusion simulations were used for studying the diffusion behavior of tracer molecules in rock matrix with homogeneous and heterogeneous porosity. As the heterogeneous sample in these simulations, a 3D tomographic image of altered tonalite was used, in which the mineral components and the pores resolved by X-ray microtomography were represented by their respective intragranular porosities determined previously by the C-PMMA method. The apparent diffusion coefficient of a tracer in altered tonalite was determined experimentally, and was then used in the simulations. In the altered tonalite analyzed, inclusion of heterogeneity in the porosity increased the diffusion coefficient by 16 %. Altered and pristine feldspar was the main mineral component in the sample (72 %), and it also provided the dominant contribution to tracer diffusion, explaining alone 52 % of the diffusion coefficient. The large pores resolved by microtomography (6 %) and altered and pristine mica (22 %) gave an equal contribution to the diffusion coefficient. The simulation method applied was also validated by comparing the results to both an analytical and a numerical solution to the diffusion equation in a homogenous medium. In addition, the method was compared to discrete-time random-walk simulations in the case of randomly placed overlapping spheres. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]