Anumaija Leskinen

Bio: Anumaija Leskinen is an academic researcher from VTT Technical Research Centre of Finland. The author has contributed to research in topics: Nuclear decommissioning & Radioactive waste. The author has an hindex of 4, co-authored 9 publications receiving 41 citations.

Tritium analysis in building dismantling process using digital autoradiography

Abstract: 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

Digital autoradiography (DA) in quantification of trace level beta emitters on concrete

Abstract: 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 m2 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 3H and 14C beta emitters. The results showed that the DA technique was a powerful tool in localization and quantification of residual radioactivity on concrete floor.

Determination of 14C, 55Fe, 63Ni and gamma emitters in activated RPV steel samples: a comparison between calculations and experimental analysis

Abstract: Determination of 14C, 55Fe, 63Ni and gamma emitters in two different types of activated reactor pressure vessel (RPV) steel samples were carried out. The gamma emitters were analysed using HPGe detectors with ISOCS and standard geometry calibrations. Two radioanalytical procedures for the 14C, 55Fe, 63Ni analysis were developed using inactive samples and activated samples were analysed using modified procedures. A Monte Carlo code was used for the modelling of the activation results. The obtained measured and calculated results were comparable.

Intercomparison exercise on difficult to measure radionuclides in activated steel: statistical analysis of radioanalytical results and activation calculations

Abstract: This paper reports the results obtained during an intercomparison exercise for the determination of difficult to measure radionuclides in activated reactor pressure vessel (RPV) steel samples. In total, eight laboratories participated analysing 14C, 55Fe and 63Ni activity concentrations in RPV steel. In addition, some laboratories also analysed 60Co activity concentrations. Corresponding activity concentrations were also determined using activation calculations. Robust statistical techniques were utilised for the analysis of the results according to ISO 13528 standard. The results showed good agreement for 55Fe and 63Ni results whereas 14C results had significant differences. 60Co results were in quite good agreement.

Characterisation of pore space geometry by 14C-PMMA impregnation - development work for in-situ studies

Abstract: Abstract In Finland, as in many other countries, high-level radioactive waste is planned to be disposed of in deep-lying crystalline rock. There has been a tendency to play down the potential role of the geosphere as a safety barrier in repository performance assessment. Among other reasons, current uncertainties in transport pathway definition and pore space characterisation of crystalline rock can be mentioned. Repository safety evaluation today requires going from laboratory and surface-based field work to the underground repository level. Little is known about the changes to rock transport properties during sampling and decompression. Recent investigations using resin impregnation of the rock matrix at the Grimsel Test Site imply that non-conservative errors in calculated transport properties derived from laboratory data may reach factors of 2/3. This may lead to over-conservative estimates of limited matrix diffusion depths, which may grossly underestimate geosphere radionuclide retardation. Due to the potentially great significance of pore space characterisation to safety analysis calculations, it was decided to study the rock matrix characteristics using an alternative resin technique. During last decade, the polymethylmethacrylate (PMMA) method has been developed for characterising the porosity of low-permeable granitic rocks in the laboratory. Impregnation with 14C-labelled methylmethacrylate (14C-MMA) and autoradiography allow investigation of the spatial distribution of accessible porosity at the centimetric scale. Quantitative measurement of total or mineral-specific local porosities have been also obtained using image analysis tools. Electron microscopy examinations and mercury porosimetry measurements have provided detailed information of pore and fissure apertures. The developments of the PMMA method for in situ testing at the Grimsel Test Site are reported here. Grimsel granodiorite samples were impregnated with MMA using various prehandling and impregnation conditions, resulting in variations of the measured porosity values. Vacuum drying of studied samples increased the PMMA and porosity values of water saturation gravimetry. If the rock matrix cannot be dried in situ, the intrusion behaviour of MMA in water filled pores will be a key consideration for successful in situ impregnation.

The characterization of radioactive waste: a critical review of techniques implemented or under development at CEA, France

Abstract: This review paper describes the destructive and non-destructive measurements implemented or under development at CEA, in view to perform the most complete radioactive waste characterization. First, high-energy photon imaging (radiography, tomography) brings essential information on the waste packages, such as density, position and shape of the waste inside the container and in the possible binder, quality of coating and blocking matrices, presence of internal shields or structures, presence of cracks, voids, or other defects in the container or in the matrix, liquids or other forbidden materials, etc. Radiological assessment is then performed using a series of non-destructive techniques such as gamma-ray spectroscopy, which allows characterizing a wide range of radioactive and nuclear materials, passive neutron coincidence counting and active neutron interrogation with the differential die-away technique, or active photon interrogation with high-energy photons (photofission), to measure nuclear materials. Prompt gamma neutron activation analysis (PGNAA) can also be employed to detect toxic chemicals or elements which can greatly influence the above measurements, such as neutron moderators or absorbers. Digital auto-radiography can also be used to detect alpha and beta contaminated waste. These non-destructive assessments can be completed by gas measurements, to quantify the radioactive and radiolysis gas releases, and by destructive examinations such as coring homogeneous waste packages or cutting the heterogeneous ones, in view to perform visual examination and a series of physical, chemical, and radiochemical analyses on samples. These last allow for instance to check the mechanical and containment properties of the package envelop, or of the waste binder, to measure toxic chemicals, to assess the activity of long-lived radionuclides or pure beta emitters, to determine the isotopic composition of nuclear materials, etc.

Calibration of digital autoradiograph technique for quantifying rock porosity using 14C-PMMA method

Abstract: Digital autoradiography (DA) based on phosphor plate imaging was tested for porosity quantification using 14C-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.

A non-destructive and on-site digital autoradiography-based tool to identify contaminating radionuclide in nuclear wastes and facilities to be dismantled

Abstract: As part of the recent developments of digital autoradiography-based methods in the context of nuclear dismantling (alpha and soft-beta on-site detection, mapping, wastes and sample characterization), two novel approaches are proposed to enable a preliminary identification of the contaminating radionuclide. An energy-storage radio luminescent phosphor screen stacking method is described, and can be completed with a comparison method between two different types of screens, for the case of non-through radiations (alpha, H-3 and C-14 beta, Fe-55 X-rays). Tests were carried out on fifteen common radionuclides as well as on real samples, and a fast stack-scan method was developed, to provide industry-ready operational tools.